Light-emitting element, display device, electronic device, and lighting device

ABSTRACT

A light-emitting element containing a light-emitting material with high light emission efficiency is provided. The light-emitting element includes a high molecular material and a guest material. The high molecular material includes at least a first high molecular chain and a second high molecular chain. The guest material has a function of exhibiting fluorescence or converting triplet excitation energy into light emission. The first high molecular chain and the second high molecular chain each include a first skeleton, a second skeleton, and a third skeleton, and the first skeleton and the second skeleton are bonded to each other through the third skeleton. The first high molecular chain and the second high molecular chain have a function of forming an excited complex.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.15/155,283, filed May 16, 2016, now U.S. Pat. No. 10,134,998, whichclaims the benefit of a foreign priority application filed in Japan asSerial No. 2015-103759 on May 21, 2015, both of which are incorporatedby reference.

TECHNICAL FIELD

One embodiment of the present invention relates to a light-emittingelement, or a display device, an electronic device, and a lightingdevice each including the light-emitting element.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of one embodiment of theinvention disclosed in this specification and the like relates to anobject, a method, or a manufacturing method. In addition, one embodimentof the present invention relates to a process, a machine, manufacture,or a composition of matter. Specifically, examples of the technicalfield of one embodiment of the present invention disclosed in thisspecification include a semiconductor device, a display device, a liquidcrystal display device, a light-emitting device, a lighting device, apower storage device, a storage device, a method of driving any of them,and a method of manufacturing any of them.

BACKGROUND ART

In recent years, research and development have been extensivelyconducted on light-emitting elements using electroluminescence (EL). Ina basic structure of such a light-emitting element, a layer containing alight-emitting substance (an EL layer) is interposed between a pair ofelectrodes. By application of a voltage between the electrodes of thiselement, light emission from the light-emitting substance can beobtained.

Since the above light-emitting element is a self-luminous type, adisplay device using this light-emitting element has advantages such ashigh visibility, no necessity of a backlight, and low power consumption.Furthermore, such a light-emitting element also has advantages in thatthe element can be manufactured to be thin and lightweight, and has highresponse speed.

In a light-emitting element whose EL layer contains an organic compoundas a light-emitting substance and is provided between a pair ofelectrodes (e.g., an organic EL element), application of a voltagebetween the pair of electrodes causes injection of electrons from acathode and holes from an anode into the EL layer having alight-emitting property and thus a current flows. By recombination ofthe injected electrons and holes, the light-emitting organic compound isbrought into an excited state to provide light emission.

As the organic compound contained in the light-emitting element, a lowmolecular compound or a high molecular compound can be used. Since thehigh molecular compound is thermally stable and can easily form a thinfilm with excellent uniformity by a coating method or the like, alight-emitting element containing the high molecular compound has beendeveloped (e.g., see Patent Document 1).

Note that an excited state formed by an organic compound can be asinglet excited state (S*) or a triplet excited state (T*). Lightemission from the singlet excited state is referred to as fluorescence,and light emission from the triplet excited state is referred to asphosphorescence. The formation ratio of S* to T* in the light-emittingelement is 1:3. In other words, a light-emitting element containing acompound emitting phosphorescence (phosphorescent compound) has higherlight emission efficiency than a light-emitting element containing acompound emitting fluorescence (fluorescent compound). Therefore,light-emitting elements containing phosphorescent compounds capable ofconverting a triplet excited state into light emission has been activelydeveloped in recent years (e.g., see Patent Document 2).

Energy needed for exciting an organic compound depends on an energydifference between the LUMO level and the HOMO level of the organiccompound, and the energy difference approximately corresponds to theenergy of the singlet excited state. In the light-emitting elementcontaining a phosphorescent compound, triplet excitation energy isconverted into light emission energy. Thus, when the energy differencebetween the singlet excited state and the triplet excited state of anorganic compound is large, the energy needed for exciting the organiccompound is higher than the light emission energy by the amountcorresponding to the energy difference. The energy difference betweenthe energy needed for exciting the organic compound and the lightemission energy increases the driving voltage in the light-emittingelement and affects element characteristics. Thus, a method for reducingthe driving voltage has been searched (see Patent Document 3).

Among light-emitting elements containing phosphorescent compounds, alight-emitting element that emits blue light in particular has yet beenput into practical use because it is difficult to develop a stablecompound having a high triplet excitation energy level. For this reason,the development of a light-emitting element containing a more stablefluorescent compound has been conducted and a technique for increasingthe light emission efficiency of a light-emitting element containing afluorescent compound (fluorescent element) has been searched.

As one of materials capable of partly converting the energy of thetriplet excited state into light emission, a thermally activated delayedfluorescent (TADF) emitter has been known. In a thermally activateddelayed fluorescent emitter, a singlet excited state is generated from atriplet excited state by reverse intersystem crossing, and the singletexcited state is converted into light emission.

In order to increase light emission efficiency of a light-emittingelement using a thermally activated delayed fluorescent emitter, notonly efficient generation of a singlet excited state from a tripletexcited state but also efficient emission from a singlet excited state,that is, a high fluorescence quantum yield is important in a thermallyactivated delayed fluorescent emitter. It is, however, difficult todesign a light-emitting material that meets these two.

Patent Document 4 discloses a method: in a light-emitting elementcontaining a thermally activated delayed fluorescent emitter and afluorescent compound, singlet excitation energy of the thermallyactivated delayed fluorescent emitter is transferred to the fluorescentcompound and light emission is obtained from the fluorescent compound.

REFERENCE Patent Documents

-   [Patent Document 1] Japanese Published Patent Application No.    H5-202355-   [Patent Document 2] Japanese Published Patent Application No.    2010-182699-   [Patent Document 3] Japanese Published Patent Application No.    2012-212879-   [Patent Document 4] Japanese Published Patent Application No.    2014-45179

DISCLOSURE OF INVENTION

In a light-emitting element containing a light-emitting organiccompound, to increase light emission efficiency or to reduce drivingvoltage, it is preferable that an energy difference between the singletexcited state and the triplet excited state of a host material be small.

In order to increase light emission efficiency of a light-emittingelement containing a fluorescent compound, efficient generation of asinglet excited state from a triplet excited state is preferable. Inaddition, efficient energy transfer from a singlet excited state of thehost material to a singlet excited state of the fluorescent compound ispreferable.

In view of the above, an object of one embodiment of the presentinvention is to provide a light-emitting element that contains afluorescent compound or a phosphorescent compound and has high lightemission efficiency. Another object of one embodiment of the presentinvention is to provide a light-emitting element with low powerconsumption. Another object of one embodiment of the present inventionis to provide a novel light-emitting element. Another object of oneembodiment of the present invention is to provide a novel light-emittingdevice. Another object of one embodiment of the present invention is toprovide a novel display device.

Note that the description of the above object does not preclude theexistence of other objects. In one embodiment of the present invention,there is no need to achieve all the objects. Objects other than theabove objects will be apparent from and can be derived from thedescription of the specification and the like.

One embodiment of the present invention is a light-emitting elementcontaining a compound which forms an excited complex efficiently.Alternatively, one embodiment of the present invention is alight-emitting element in which a triplet exciton is converted into asinglet exciton and light can be emitted from a compound containing thesinglet exciton or light can be emitted from a fluorescent compound dueto energy transfer of the singlet exciton.

Thus, one embodiment of the present invention is a light-emittingelement including a high molecular material and a guest material. Thehigh molecular material includes at least a first high molecular chainand a second high molecular chain. The guest material has a function ofexhibiting fluorescence. The first high molecular chain and the secondhigh molecular chain each include a first skeleton, a second skeleton,and a third skeleton. The first skeleton and the second skeleton arebonded to each other through the third skeleton. The first skeleton hasa function of transferring holes. The second skeleton has a function oftransferring electrons. The first high molecular chain and the secondhigh molecular chain have a function of forming an excited complex.

Another embodiment of the present invention is a light-emitting elementincluding a high molecular material and a guest material. The highmolecular material includes at least a first high molecular chain and asecond high molecular chain. The guest material has a function ofconverting triplet excitation energy into light emission. The first highmolecular chain and the second high molecular chain each include a firstskeleton, a second skeleton, and a third skeleton. The first skeletonand the second skeleton are bonded to each other through the thirdskeleton. The first skeleton has a function of transferring holes. Thesecond skeleton has a function of transferring electrons. The first highmolecular chain and the second high molecular chain have a function offorming an excited complex.

Another embodiment of the present invention is a light-emitting elementincluding a high molecular material. The high molecular materialincludes at least a first high molecular chain and a second highmolecular chain. The first high molecular chain and the second highmolecular chain each include a first skeleton, a second skeleton, athird skeleton, and a fourth skeleton. The first skeleton and the secondskeleton are bonded to each other through the third skeleton. The firstskeleton has a function of transferring holes. The second skeleton has afunction of transferring electrons. The fourth skeleton has a functionof exhibiting fluorescence. The first high molecular chain and thesecond high molecular chain have a function of forming an excitedcomplex.

Another embodiment of the present invention is a light-emitting elementincluding a high molecular material. The high molecular materialincludes at least a first high molecular chain and a second highmolecular chain. The first high molecular chain and the second highmolecular chain each include a first skeleton, a second skeleton, athird skeleton, and a fourth skeleton. The first skeleton and the secondskeleton are bonded to each other through the third skeleton. The firstskeleton has a function of transferring holes. The second skeleton has afunction of transferring electrons. The fourth skeleton has a functionof converting triplet excitation energy into light emission. The firsthigh molecular chain and the second high molecular chain have a functionof forming an excited complex.

Another embodiment of the present invention is a light-emitting elementincluding a high molecular material and a guest material. The highmolecular material includes at least a first high molecular chain and asecond high molecular chain. The guest material has a function ofexhibiting fluorescence. The first high molecular chain and the secondhigh molecular chain each include a first skeleton, a second skeleton,and a third skeleton. The first skeleton and the second skeleton arebonded to each other through the third skeleton. The first skeletonincludes at least one of a π-electron rich heteroaromatic skeleton andan aromatic amine skeleton. The second skeleton includes a π-electrondeficient heteroaromatic skeleton. The first high molecular chain andthe second high molecular chain have a function of forming an excitedcomplex.

Another embodiment of the present invention is a light-emitting elementincluding a high molecular material and a guest material. The highmolecular material includes at least a first high molecular chain and asecond high molecular chain. The guest material has a function ofconverting triplet excitation energy into light emission. The first highmolecular chain and the second high molecular chain each include a firstskeleton, a second skeleton, and a third skeleton. The first skeletonand the second skeleton are bonded to each other through the thirdskeleton. The first skeleton includes at least one of a π-electron richheteroaromatic skeleton and an aromatic amine skeleton. The secondskeleton includes a π-electron deficient heteroaromatic skeleton. Thefirst high molecular chain and the second high molecular chain have afunction of forming an excited complex.

Another embodiment of the present invention is a light-emitting elementincluding a high molecular material. The high molecular materialincludes at least a first high molecular chain and a second highmolecular chain. The first high molecular chain and the second highmolecular chain each include a first skeleton, a second skeleton, athird skeleton, and a fourth skeleton. The first skeleton and the secondskeleton are bonded to each other through the third skeleton. The firstskeleton includes at least one of a π-electron rich heteroaromaticskeleton and an aromatic amine skeleton. The second skeleton includes aπ-electron deficient heteroaromatic skeleton. The fourth skeleton has afunction of exhibiting fluorescence. The first high molecular chain andthe second high molecular chain have a function of forming an excitedcomplex.

Another embodiment of the present invention is a light-emitting elementincluding a high molecular material. The high molecular materialincludes at least a first high molecular chain and a second highmolecular chain. The first high molecular chain and the second highmolecular chain each include a first skeleton, a second skeleton, athird skeleton, and a fourth skeleton. The first skeleton and the secondskeleton are bonded to each other through the third skeleton. The firstskeleton includes at least one of a π-electron rich heteroaromaticskeleton and an aromatic amine skeleton. The second skeleton includes aπ-electron deficient heteroaromatic skeleton. The fourth skeleton has afunction of converting triplet excitation energy into light emission.The first high molecular chain and the second high molecular chain havea function of forming an excited complex.

In each of the above structures, the π-electron rich heteroaromaticskeleton preferably includes at least one of a thiophene skeleton, afuran skeleton, and a pyrrole skeleton. The π-electron deficientheteroaromatic skeleton preferably includes at least one of a pyridineskeleton, a diazine skeleton, and a triazine skeleton. The thirdskeleton preferably includes at least one of a biphenyl skeleton and afluorene skeleton.

In each of the above structures, the first high molecular chain and thesecond high molecular chain have a function of forming the excitedcomplex with the first skeleton in the first high molecular chain andthe second skeleton in the second high molecular chain. In addition, theexcited complex preferably has a function of exhibiting thermallyactivated delayed fluorescence at room temperature.

Another embodiment of the present invention is a display deviceincluding the light-emitting element having any of the above-describedstructures, and at least one of a color filter and a transistor. Anotherembodiment of the present invention is an electronic device includingthe above-described display device and at least one of a housing and atouch sensor. Another embodiment of the present invention is a lightingdevice including the light-emitting element having any of theabove-described structures, and at least one of a housing and a touchsensor. The category of one embodiment of the present invention includesnot only a light-emitting device including a light-emitting element butalso an electronic device including a light-emitting device. Thus, thelight-emitting device in this specification refers to an image displaydevice and a light source (e.g., a lighting device). The light-emittingdevice may be included in a module in which a connector such as aflexible printed circuit (FPC) or a tape carrier package (TCP) isconnected to a light-emitting device, a module in which a printed wiringboard is provided on the tip of a TCP, or a module in which anintegrated circuit (IC) is directly mounted on a light-emitting elementby a chip on glass (COG) method.

With one embodiment of the present invention, a light-emitting elementcontaining a fluorescent compound or a phosphorescent compound which hashigh light emission efficiency can be provided. With one embodiment ofthe present invention, a light-emitting element with low powerconsumption can be provided. With one embodiment of the presentinvention, a novel light-emitting element can be provided. With oneembodiment of the present invention, a novel light-emitting device canbe provided. With one embodiment of the present invention, a noveldisplay device can be provided.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily have all the effects described above. Other effects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are schematic cross-sectional views of a light-emittingelement of one embodiment of the present invention and FIG. 1Cillustrates the correlation of energy levels in a light-emitting layer;

FIG. 2 is a schematic cross-sectional view of a light-emitting layer ofone embodiment of the present invention;

FIGS. 3A and 3B are schematic cross-sectional views of a light-emittingelement of one embodiment of the present invention and FIG. 3Cillustrates the correlation of energy levels in a light-emitting layer;

FIG. 4 is a schematic cross-sectional view of a light-emitting layer ofone embodiment of the present invention;

FIGS. 5A and 5B are each a schematic cross-sectional view of alight-emitting element of one embodiment of the present invention;

FIGS. 6A and 6B are each a schematic cross-sectional view of alight-emitting element of one embodiment of the present invention;

FIGS. 7A to 7C are schematic cross-sectional views illustrating a methodfor manufacturing a light-emitting element of one embodiment of thepresent invention;

FIGS. 8A and 8B are schematic cross-sectional views illustrating amethod for manufacturing a light-emitting element of one embodiment ofthe present invention;

FIGS. 9A and 9B are a top view and a schematic cross-sectional viewillustrating a display device of one embodiment of the presentinvention;

FIGS. 10A and 10B are schematic cross-sectional views each illustratinga display device of one embodiment of the present invention;

FIG. 11 is a schematic cross-sectional view illustrating a displaydevice of one embodiment of the present invention;

FIGS. 12A and 12B are schematic cross-sectional views each illustratinga display device of one embodiment of the present invention;

FIGS. 13A and 13B are schematic cross-sectional views each illustratinga display device of one embodiment of the present invention;

FIG. 14 is a schematic cross-sectional view illustrating a displaydevice of one embodiment of the present invention;

FIGS. 15A and 15B are schematic cross-sectional views each illustratinga display device of one embodiment of the present invention;

FIG. 16 is a schematic cross-sectional view illustrating a displaydevice of one embodiment of the present invention;

FIGS. 17A and 17B are schematic cross-sectional views each illustratinga display device of one embodiment of the present invention;

FIGS. 18A to 18D are schematic cross-sectional views illustrating amethod for forming an EL layer;

FIG. 19 is a conceptual diagram illustrating a droplet dischargeapparatus;

FIGS. 20A and 20B are a block diagram and a circuit diagram illustratinga display device of one embodiment of the present invention;

FIGS. 21A and 21B are circuit diagrams each illustrating a pixel circuitof a display device of one embodiment of the present invention;

FIGS. 22A and 22B are circuit diagrams each illustrating a pixel circuitof a display device of one embodiment of the present invention;

FIGS. 23A and 23B are perspective views of an example of a touch panelof one embodiment of the present invention;

FIGS. 24A to 24C are cross-sectional views of examples of a displaydevice and a touch sensor of one embodiment of the present invention;

FIGS. 25A and 25B are cross-sectional views of examples of a touch panelof one embodiment of the present invention;

FIGS. 26A and 26B are a block diagram and a timing chart of a touchsensor of one embodiment of the present invention;

FIG. 27 is a circuit diagram of a touch sensor of one embodiment of thepresent invention;

FIG. 28 is a perspective view illustrating a display module of oneembodiment of the present invention;

FIGS. 29A to 29G illustrate electronic devices of one embodiment of thepresent invention;

FIGS. 30A to 30D illustrate electronic devices of one embodiment of thepresent invention;

FIGS. 31A and 31B are perspective views illustrating a display device ofone embodiment of the present invention;

FIGS. 32A to 32C are a perspective view and cross-sectional viewsillustrating light-emitting devices of one embodiment of the presentinvention;

FIGS. 33A to 33D are cross-sectional views each illustrating alight-emitting device of one embodiment of the present invention;

FIGS. 34A to 34C illustrate an electronic device and a lighting deviceof one embodiment of the present invention; and

FIG. 35 illustrates lighting devices of one embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings. However, the present invention is not limitedto description to be given below, and it is to be easily understood thatmodes and details thereof can be variously modified without departingfrom the purpose and the scope of the present invention. Accordingly,the present invention should not be interpreted as being limited to thecontent of the embodiments below.

Note that the position, the size, the range, or the like of eachstructure illustrated in drawings and the like is not accuratelyrepresented in some cases for simplification. Therefore, the disclosedinvention is not necessarily limited to the position, the size, therange, or the like disclosed in the drawings and the like.

Note that the ordinal numbers such as “first”, “second”, and the like inthis specification and the like are used for convenience and do notdenote the order of steps or the stacking order of layers. Therefore,for example, description can be made even when “first” is replaced with“second” or “third”, as appropriate. In addition, the ordinal numbers inthis specification and the like are not necessarily the same as thosewhich specify one embodiment of the present invention.

In the description of modes of the present invention in thisspecification and the like with reference to the drawings, the samecomponents in different diagrams are commonly denoted by the samereference numeral in some cases.

In this specification and the like, the terms “film” and “layer” can beinterchanged with each other depending on the case or circumstances. Forexample, the term “conductive layer” can be changed into the term“conductive film” in some cases. Also, the term “insulating film” can bechanged into the term “insulating layer” in some cases.

In this specification and the like, a singlet excited state (S*) refersto a singlet state having excitation energy. An S1 level means thelowest level of the singlet excitation energy, that is, the lowest levelof excitation energy in a singlet excited state. A triplet excited state(T*) refers to a triplet state having excitation energy. A T1 levelmeans the lowest level of the triplet excitation energy, that is, thelowest level of excitation energy in a triplet excited state.

In this specification and the like, a fluorescent compound refers to acompound that emits light in the visible light region when therelaxation from the singlet excited state to the ground state occurs. Aphosphorescent compound refers to a compound that emits light in thevisible light region at room temperature when the relaxation from thetriplet excited state to the ground state occurs. That is, aphosphorescent compound refers to a compound that can convert tripletexcitation energy into visible light.

Thermally activated delayed fluorescence emission energy refers to anemission peak (including a shoulder) on the shortest wavelength side ofthermally activated delayed fluorescence. Phosphorescence emissionenergy or triplet excitation energy refers to an emission peak(including a shoulder) on the shortest wavelength side ofphosphorescence emission. Note that the phosphorescence emission can beobserved by time-resolved photoluminescence in a low-temperature (e.g.,10 K) environment.

Note that in this specification and the like, “room temperature” refersto a temperature higher than or equal to 0° C. and lower than or equalto 40° C.

In this specification and the like, a high molecular material and a highmolecular compound are each a polymer which has molecular weightdistribution and whose average molecular weight is 1×10³ to 1×10⁸. A lowmolecular compound is a compound which does not have molecular weightdistribution and whose molecular weight is less than or equal to 1×10⁴.

In addition, the high molecular material and the high molecular compoundare a material and a compound in which one kind of structural units orplural kinds of structural units are polymerized. That is, thestructural unit refers to a unit at least one of which is included ineach of the high molecular material and the high molecular compound.

In addition, the high molecular material and the high molecular compoundmay each be any of a block copolymer, a random copolymer, an alternatingcopolymer, and a graft copolymer, or another embodiment.

In the case where an end group of each of the high molecular materialand the high molecular compound includes a polymerization active group,light emission characteristics and luminance lifetime of thelight-emitting element may be reduced. Thus, the end group of each ofthe high molecular material and the high molecular compound ispreferably a stable end group. As the stable end group, a group which iscovalently bonded to a main chain is preferable, and a group which isbonded to an aryl group or a heterocycle group through a carbon-carbonbond is particularly preferable.

In this specification and the like, a wavelength range of blue refers toa wavelength range of greater than or equal to 400 nm and less than 490nm, and blue light emission refers to light emission with at least oneemission spectrum peak in the wavelength range. A wavelength range ofgreen refers to a wavelength range of greater than or equal to 490 nmand less than 580 nm, and green light emission refers to light emissionwith at least one emission spectrum peak in the wavelength range. Awavelength range of red refers to a wavelength range of greater than orequal to 580 nm and less than or equal to 680 nm, and red light emissionrefers to light emission with at least one emission spectrum peak in thewavelength range.

Embodiment 1

In this embodiment, a light-emitting element of one embodiment of thepresent invention will be described below with reference to FIGS. 1A to1C and FIG. 2.

Structure Example 1 of Light-Emitting Element

First, a structure of the light-emitting element of one embodiment ofthe present invention will be described below with reference to FIGS. 1Ato 1C.

FIG. 1A is a schematic cross-sectional view of a light-emitting element150 of one embodiment of the present invention.

The light-emitting element 150 includes a pair of electrodes (anelectrode 101 and an electrode 102) and an EL layer 100 between the pairof electrodes. The EL layer 100 includes at least a light-emitting layer130.

The EL layer 100 illustrated in FIG. 1A includes functional layers suchas a hole-injection layer 111 and an electron-injection layer 114, inaddition to the light-emitting layer 130.

Although description is given assuming that the electrode 101 and theelectrode 102 of the pair of electrodes serve as an anode and a cathode,respectively in this embodiment, the structure of the light-emittingelement 150 is not limited thereto. That is, the electrode 101 may be acathode, the electrode 102 may be an anode, and the stacking order ofthe layers between the electrodes may be reversed. In other words, thehole-injection layer 111, the light-emitting layer 130, and theelectron-injection layer 114 may be stacked in this order from the anodeside.

The structure of the EL layer 100 is not limited to the structureillustrated in FIG. 1A, and a structure including at least one layerselected from the hole-injection layer 111 and the electron-injectionlayer 114 may be employed. Alternatively, the EL layer 100 may include afunctional layer which is capable of lowering a hole- orelectron-injection barrier, improving a hole- or electron-transportproperty, inhibiting a hole- or electron-transport property, orsuppressing a quenching phenomenon by an electrode, for example. Notethat the functional layers may each be a single layer or stacked layers.

FIG. 1B is a schematic cross-sectional view illustrating an example ofthe light-emitting layer 130 in FIG. 1A. The light-emitting layer 130 inFIG. 1B includes a high molecular material 131 and a guest material 132.

The high molecular material 131 includes a skeleton 131_1, a skeleton131_2, and a skeleton 131_3 as structural units. The skeleton 131_1 andthe skeleton 131_2 are bonded or polymerized to each other through theskeleton 131_3.

The guest material 132 may be a light-emitting organic compound, and thelight-emitting organic compound is preferably a substance capable ofemitting fluorescence (hereinafter also referred to as a fluorescentcompound). A structure in which a fluorescent compound is used as theguest material 132 will be described below. The guest material 132 maybe rephrased as the fluorescent compound.

In the light-emitting element 150 of one embodiment of the presentinvention, voltage application between the pair of electrodes (theelectrodes 101 and 102) allows electrons and holes to be injected fromthe cathode and the anode, respectively, into the EL layer 100 and thuscurrent flows. By recombination of the injected electrons and holes,excitons are formed. The ratio of singlet excitons to triplet excitons(hereinafter referred to as exciton generation probability) which aregenerated by the carrier (electrons and holes) recombination isapproximately 1:3 according to the statistically obtained probability.Accordingly, in a light-emitting element that contains a fluorescentcompound, the probability of generation of singlet excitons, whichcontribute to light emission, is 25% and the probability of generationof triplet excitons, which do not contribute to light emission, is 75%.Therefore, it is important to convert the triplet excitons, which do notcontribute to light emission, into singlet excitons, which contribute tolight emission, for increasing the light emission efficiency of thelight-emitting element.

Thus, the high molecular material 131 preferably has a function ofgenerating the singlet excited state from the triplet excited state.

<Light Emission Mechanism of Light-Emitting Element>

Next, the light emission mechanism of the light-emitting layer 130 isdescribed below.

In the high molecular material 131 in the light-emitting layer 130, itis preferable that the skeleton 131_1 include a skeleton having afunction of transporting holes (a hole-transport property) and theskeleton 131_2 include a skeleton having a function of transportingelectrons (an electron-transport property). Alternatively, it ispreferable that the skeleton 131_1 include at least one of a π-electronrich heteroaromatic skeleton and an aromatic amine skeleton and theskeleton 131_2 include a π-electron deficient heteroaromatic skeleton.

In one embodiment of the present invention, the high molecular material131 has a function of forming an excited complex (also referred to as anexcited dimer) with two high molecular chains of the high molecularmaterial 131. In particular, the skeleton having a hole-transportproperty and the skeleton having an electron-transport property of thehigh molecular material 131 preferably form an excited complex in twohigh molecular chains including the same structural units.Alternatively, at least one of the π-electron rich heteroaromaticskeleton and the aromatic amine skeleton included in the high molecularmaterial 131 and the π-electron deficient heteroaromatic skeletonincluded in the high molecular material 131 preferably form an excitedcomplex in two high molecular chains including the same structuralunits. Note that in this specification and the like, the high molecularchains including the same structural units are high molecular chainswhich include at least the same kinds of structural units (here, theskeleton 131_1, the skeleton 131_2, and the skeleton 131_3), and mayhave different bond directions, bond angles, bond lengths, and the likeof the structural units. In addition, the structural units may havedifferent substituents, and different skeletons may be provided betweenthe structural units. In addition, polymerization methods of thestructural units may be different.

In other words, the high molecular material 131 has a function offorming an excited complex with a first high molecular chain and asecond high molecular chain of the high molecular material 131. Inparticular, the skeleton having a hole-transport property in the firsthigh molecular chain and the skeleton having an electron-transportproperty in the second high molecular chain of the high molecularmaterial 131 preferably form an excited complex. Alternatively, at leastone of the π-electron rich heteroaromatic skeleton and the aromaticamine skeleton in the first high molecular chain of the high molecularmaterial 131 and the π-electron deficient heteroaromatic skeleton in thesecond high molecular chain of the high molecular material 131preferably form an excited complex.

In the case where the high molecular material 131 includes the skeletonhaving a hole-transport property included in the skeleton 131_1 and theskeleton having an electron-transport property included in the skeleton131_2, a donor-acceptor excited complex is easily formed by two highmolecular chains; thus, efficient formation of an excited complex ispossible. Alternatively, in the case where the high molecular material131 includes at least one of the π-electron rich heteroaromatic skeletonand the aromatic amine skeleton included in the skeleton 131_1, and theπ-electron deficient heteroaromatic skeleton included in the skeleton131_2, a donor-acceptor excited complex is easily formed by two highmolecular chains; thus, efficient formation of an excited complex ispossible.

Thus, to increase both the donor property and the acceptor property inthe high molecular chains of the high molecular material 131, astructure where the conjugation between the skeleton having ahole-transport property and the skeleton having an electron-transportproperty is reduced is preferably used. Alternatively, a structure wherethe conjugation between the π-electron deficient heteroaromatic skeletonand at least one of the π-electron rich heteroaromatic skeleton and thearomatic amine skeleton is reduced is preferably used. Thus, an overlapbetween a region where the highest occupied molecular orbital (HOMO) isdistributed and a region where the lowest unoccupied molecular orbital(LUMO) is distributed can be small. In addition, a difference between asinglet excitation energy level and a triplet excitation energy level ofthe high molecular material 131 can be reduced. Moreover, the tripletexcitation energy level of the high molecular material 131 can be high.

Note that a molecular orbital refers to spatial distribution ofelectrons in a molecule, and can show the probability of finding ofelectrons. In addition, with the molecular orbital, electronconfiguration of the molecule (spatial distribution and energy ofelectrons) can be described in detail.

Furthermore, in the excited complex formed by the two high molecularchains including the same structural units, one high molecular chainincludes the HOMO and the other high molecular chain includes the LUMO;thus, an overlap between the HOMO and the LUMO is extremely small. Thatis, in the excited complex, a difference between a singlet excitationenergy level and a triplet excitation energy level is small. Therefore,in the excited complex formed by the two high molecular chains of thehigh molecular material 131, a difference between a singlet excitationenergy level and a triplet excitation energy level is small and ispreferably larger than 0 eV and smaller than or equal to 0.2 eV.

In the case where the high molecular material 131 includes the skeletonhaving a hole-transport property and the skeleton having anelectron-transport property, the carrier balance can be easilycontrolled. As a result, a carrier recombination region can also becontrolled easily. In order to achieve this, it is preferable that thecomposition ratio of the skeleton 131_1 (including the skeleton having ahole-transport property) to the skeleton 131_2 (including the skeletonhaving an electron-transport property) be in the range of 1:9 to 9:1(molar ratio), and it is further preferable that the proportion of theskeleton 131_2 (including the skeleton having an electron-transportproperty) be higher than the proportion of the skeleton 131_1 (includingthe skeleton having a hole-transport property).

FIG. 1C shows a correlation of energy levels of the high molecularmaterial 131 and the guest material 132 in the light-emitting layer 130.The following explains what terms and signs in FIG. 1C represent:

Polymer (131_1+131_2): the skeleton 131_1 in the first high molecularchain and the skeleton 131_2 in the second high molecular chain, whichare close to each other, of the high molecular material 131;

Guest (132): the guest material 132 (the fluorescent compound);

S_(H): the S1 level of the high molecular material 131;

T_(H): the T1 level of the high molecular material 131;

S_(G): the S1 level of the guest material 132 (the fluorescentcompound);

T_(G): the T1 level of the guest material 132 (the fluorescentcompound);

S_(E): the S1 level of the excited complex; and

T_(E): the T1 level of the excited complex.

In the light-emitting layer 130, the high molecular material 131 ispresent in the largest proportion by weight, and the guest material 132(the fluorescent compound) is dispersed in the high molecular material131. The S1 level of the high molecular material 131 in thelight-emitting layer 130 is preferably higher than the S1 level of theguest material 132 (the fluorescent compound) in the light-emittinglayer 130. The T1 level of the high molecular material 131 in thelight-emitting layer 130 is preferably higher than the T1 level of theguest material 132 (the fluorescent compound) in the light-emittinglayer 130.

In the light-emitting element of one embodiment of the presentinvention, an excited complex is formed by the two high molecular chainsof the high molecular material 131 included in the light-emitting layer130. The lowest singlet excitation energy level (S_(E)) of the excitedcomplex and the lowest triplet excitation energy level (T_(E)) of theexcited complex are close to each other (see Route E₃ in FIG. 1C).

An excited complex is an excited state formed by two high molecularchains. In photoexcitation, the excited complex is formed by interactionbetween one high molecular chain in an excited state and the other highmolecular chain in a ground state. The two high molecular chains thathave formed the excited complex return to a ground state by emittinglight and then serve as the original two high molecular chains. Inelectrical excitation, one high molecular chain brought into an excitedstate immediately interacts with the other high molecular chain to forman excited complex. Alternatively, one high molecular chain receives ahole and the other high molecular chain receives an electron toimmediately form an excited complex. In this case, any of the highmolecular chains can form an excited complex without forming an excitedstate with a single high molecular chain and; accordingly, most excitonsin the light-emitting layer 130 can exist as excited complexes. Becausethe excitation energy levels (S_(E) and T_(E)) of the excited complexare lower than the singlet excitation energy level (S_(H)) of a singlehigh molecular chain of the high molecular material 131 that forms theexcited complex, the excited state of the high molecular material 131can be formed with lower excitation energy. Accordingly, the drivingvoltage of the light-emitting element 150 can be reduced.

Since the singlet excitation energy level (S_(E)) and the tripletexcitation energy level (T_(E)) of the excited complex are close to eachother, the excited complex has a function of exhibiting thermallyactivated delayed fluorescence. In other words, the excited complex hasa function of converting triplet excitation energy into singletexcitation energy by reverse intersystem crossing (upconversion) (seeRoute E₄ in FIG. 1C). Thus, the triplet excitation energy generated inthe light-emitting layer 130 is partly converted into singlet excitationenergy by the excited complex. In order to cause this conversion, theenergy difference between the singlet excitation energy level (S_(E))and the triplet excitation energy level (T_(E)) of the excited complexis preferably larger than 0 eV and smaller than or equal to 0.2 eV.

Furthermore, the singlet excitation energy level (S_(E)) of the excitedcomplex is preferably higher than the singlet excitation energy level(S_(G)) of the guest material 132. In this way, the singlet excitationenergy of the formed excited complex can be transferred from the singletexcitation energy level (S_(E)) of the excited complex to the singletexcitation energy level (S_(G)) of the guest material 132, so that theguest material 132 is brought into the singlet excited state, causinglight emission (see Route E₅ in FIG. 1C).

To obtain efficient light emission from the singlet excited state of theguest material 132, the fluorescence quantum yield of the guest material132 is preferably high, and specifically, 50% or higher, furtherpreferably 70% or higher, still further preferably 90% or higher.

Note that in order to efficiently make reverse intersystem crossingoccur, the triplet excitation energy level (T_(E)) of the excitedcomplex formed by two high molecular chains is preferably lower than thetriplet excitation energy level (T_(H)) of the single high molecularchain of the high molecular material 131 which forms the excitedcomplex. Thus, quenching of the triplet excitation energy of the excitedcomplex due to another one or more high molecular chains in the highmolecular material 131 is less likely to occur, which causes reverseintersystem crossing efficiently.

Thus, the triplet excitation energy level of the high molecular material131 is preferably high, and the energy difference between the singletexcitation energy level and the triplet excitation energy level of thehigh molecular material 131 is preferably small.

Note that since direct transition from a singlet ground state to atriplet excited state in the guest material 132 is forbidden, energytransfer from the singlet excitation energy level (S_(E)) of the excitedcomplex to the triplet excitation energy level (T_(G)) of the guestmaterial 132 is unlikely to be a main energy transfer process.

When transfer of the triplet excitation energy from the tripletexcitation energy level (T_(E)) of the excited complex to the tripletexcitation energy level (T_(G)) of the guest material 132 occurs, thetriplet excitation energy is deactivated (see Route E₆ in FIG. 1C).Thus, it is preferable that the energy transfer of Route E₆ be lesslikely to occur because the efficiency of generating the triplet excitedstate of the guest material 132 can be decreased and thermaldeactivation can be reduced. In order to make this condition, the weightratio of the guest material 132 to the high molecular material 131 ispreferably low, specifically, preferably greater than or equal to 0.001and less than or equal to 0.05, further preferably greater than or equalto 0.001 and less than or equal to 0.03, further preferably greater thanor equal to 0.001 and less than or equal to 0.01.

Note that when the direct carrier recombination process in the guestmaterial 132 is dominant, a large number of triplet excitons aregenerated in the light-emitting layer 130, resulting in decreased lightemission efficiency due to thermal deactivation. Thus, it is preferablethat the probability of the energy transfer process through the excitedcomplex formation process (Routes E₄ and E₅ in FIG. 1C) be higher thanthe probability of the direct carrier recombination process in the guestmaterial 132 because the efficiency of generating the triplet excitedstate of the guest material 132 can be decreased and thermaldeactivation can be reduced. Therefore, as described above, the weightratio of the guest material 132 to the high molecular material 131 ispreferably low, specifically, preferably greater than or equal to 0.001and less than or equal to 0.05, further preferably greater than or equalto 0.001 and less than or equal to 0.03, further preferably greater thanor equal to 0.001 and less than or equal to 0.01.

By making all the energy transfer processes of Routes E₄ and E₅efficiently occur in the above-described manner, both the singletexcitation energy and the triplet excitation energy of the highmolecular material 131 can be efficiently converted into the singletexcitation energy of the guest material 132, whereby the light-emittingelement 150 can emit light with high light emission efficiency.

Since an excited complex is called “an exciplex” in some cases, theabove-described processes through Routes E₃, E₄, and E₅ may be referredto as exciplex-singlet energy transfer (ExSET) or exciplex-enhancedfluorescence (ExEF) in this specification and the like. In other words,in the light-emitting layer 130, excitation energy is transferred fromthe excited complex to the guest material 132.

When the light-emitting layer 130 has the above-described structure,light emission from the guest material 132 of the light-emitting layer130 can be obtained efficiently.

As the material having a function of generating a singlet excited statefrom a triplet excited state, a thermally activated delayed fluorescent(TADF) material is known. The TADF material can generate the singletexcited state by itself from the triplet excited state by reverseintersystem crossing. In other words, the TADF material has a functionof partly converting the energy of the triplet excitation energy intolight emission.

Thus, the TADF material has a small difference between the tripletexcitation energy level and the singlet excitation energy level and canup-convert the triplet excited state into a singlet excited state withlittle thermal energy. Specifically, the difference between the tripletexcitation energy level and the singlet excitation energy level ispreferably larger than 0 eV and smaller than or equal to 0.2 eV, furtherpreferably larger than 0 eV and smaller than or equal to 0.1 eV.

As an example of the TADF material, a heterocyclic compound including aπ-electron rich heteroaromatic skeleton and a π-electron deficientheteroaromatic skeleton is given. To make the heterocyclic compound havea function of exhibiting thermally activated delayed fluorescence, it ispreferable that the π-electron rich heteroaromatic skeleton and theπ-electron deficient heteroaromatic skeleton be directly bonded to eachother and thus both the donor property of the π-electron richheteroaromatic skeleton and the acceptor property of the π-electrondeficient heteroaromatic skeleton be increased. Furthermore, it ispreferable that the conjugation between the π-electron richheteroaromatic skeleton and the π-electron deficient heteroaromaticskeleton be reduced and an overlap between the HOMO and the LUMO bereduced. However, it is preferable that a certain overlap between theHOMO and the LUMO be provided to increase probability of transition(oscillator strength) between the HOMO and the LUMO. In this manner, thedifference between the singlet excitation energy level and the tripletexcitation energy level can be reduced and light emission from thesinglet excited state can be efficiently obtained.

For such a heterocyclic compound, a structure where the π-electron richheteroaromatic skeleton, such as an acridine skeleton, a phenazineskeleton, and a phenoxazine skeleton, has a strong twist in a portionbonded to the π-electron deficient heteroaromatic skeleton, and theconjugation between the π-electron rich heteroaromatic skeleton and theπ-electron deficient heteroaromatic skeleton is reduced is preferablyused. However, the molecular structure of a skeleton having such a twiststructure is limited.

Thus, in one embodiment of the present invention, it is preferable that,in the high molecular material 131, the skeleton 131_1 having ahole-transport property and the skeleton 131_2 having anelectron-transport property be bonded or polymerized to each otherthrough the skeleton 131_3. Alternatively, it is preferable that, in thehigh molecular material 131, the π-electron deficient heteroaromaticskeleton and at least one of the π-electron rich heteroaromatic skeletonand the aromatic amine skeleton be bonded or polymerized to each otherthrough the skeleton 131_3. Note that the detail of the skeleton 131_3will be described later.

<Energy Transfer Mechanism>

Next, factors controlling the processes of intermolecular energytransfer between the high molecular material 131 and the guest material132 will be described. As mechanisms of the intermolecular energytransfer, two mechanisms, i.e., Förster mechanism (dipole-dipoleinteraction) and Dexter mechanism (electron exchange interaction), havebeen proposed. Although the intermolecular energy transfer processbetween the high molecular material 131 and the guest material 132 isdescribed here, the same can apply to a case where the high molecularmaterial 131 forms an excited complex.

<<Förster Mechanism>>

In Förster mechanism, energy transfer does not require direct contactbetween molecules and energy is transferred through a resonantphenomenon of dipolar oscillation between the high molecular material131 and the guest material 132. By the resonant phenomenon of dipolaroscillation, the high molecular material 131 provides energy to theguest material 132, and thus, the high molecular material 131 in anexcited state is brought to a ground state and the guest material 132 ina ground state is brought to an excited state. Note that the rateconstant k_(h*→g) of Förster mechanism is expressed by Formula (1).

$\begin{matrix}{k_{h^{*}\rightarrow g} = {\frac{9000\; c^{4}K^{2}\phi\;\ln\; 10}{128\pi^{5}n^{4}N\;\tau\; R^{6}}{\int{\frac{{f_{h}^{\prime}(v)}{ɛ_{g}(v)}}{v^{4}}{dv}}}}} & (1)\end{matrix}$

In Formula (1), v denotes a frequency, f′_(h)(v) denotes a normalizedemission spectrum of the high molecular material 131 (a fluorescentspectrum in energy transfer from a singlet excited state, and aphosphorescent spectrum in energy transfer from a triplet excitedstate), ε_(g)(v) denotes a molar absorption coefficient of the guestmaterial 132, N denotes Avogadro's number, n denotes a refractive indexof a medium, R denotes an intermolecular distance between the highmolecular material 131 and the guest material 132, τ denotes a measuredlifetime of an excited state (fluorescence lifetime or phosphorescencelifetime), c denotes the speed of light, ϕ denotes a luminescencequantum yield (a fluorescence quantum yield in energy transfer from asinglet excited state, and a phosphorescence quantum yield in energytransfer from a triplet excited state), and K² denotes a coefficient (0to 4) of orientation of a transition dipole moment between the highmolecular material 131 and the guest material 132. Note that K² is ⅔ inrandom orientation.

<<Dexter Mechanism>>

In Dexter mechanism, the high molecular material 131 and the guestmaterial 132 are close to a contact effective range where their orbitalsoverlap, and the high molecular material 131 in an excited state and theguest material 132 in a ground state exchange their electrons, whichleads to energy transfer. Note that the rate constant k_(h*→g) of Dextermechanism is expressed by Formula (2).

$\begin{matrix}{k_{h^{*}\rightarrow g} = {\left( \frac{2\pi}{h} \right)K^{2}{\exp\left( {- \frac{2\; R}{L}} \right)}{\int{{f_{h}^{\prime}(v)}{ɛ_{g}^{\prime}(v)}{dv}}}}} & (2)\end{matrix}$

In Formula (2), h denotes a Planck constant, K denotes a constant havingan energy dimension, v denotes a frequency, f′_(h)(v) denotes anormalized emission spectrum of the high molecular material 131 (afluorescent spectrum in energy transfer from a singlet excited state,and a phosphorescent spectrum in energy transfer from a triplet excitedstate), ε′_(g)(v) denotes a normalized absorption spectrum of the guestmaterial 132, L denotes an effective molecular radius, and R denotes anintermolecular distance between the high molecular material 131 and theguest material 132.

Here, the efficiency of energy transfer from the high molecular material131 to the guest material 132 (energy transfer efficiency ϕ_(ET)) isexpressed by Formula (3). In the formula, k_(r) denotes a rate constantof a light-emission process (fluorescence in energy transfer from asinglet excited state, and phosphorescence in energy transfer from atriplet excited state) of the high molecular material 131, k_(n) denotesa rate constant of a non-light-emission process (thermal deactivation orintersystem crossing) of the high molecular material 131, and τ denotesa measured lifetime of an excited state of the high molecular material131.

$\begin{matrix}{\phi_{ET} = {\frac{k_{h^{*}\rightarrow g}}{k_{r} + k_{n} + k_{h^{*}\rightarrow g}} = \frac{k_{h^{*}\rightarrow g}}{\left( \frac{1}{\tau} \right) + k_{h^{*}\rightarrow g}}}} & (3)\end{matrix}$

According to Formula (3), it is found that the energy transferefficiency ϕ_(ET) can be increased by increasing the rate constantk_(h*→g) of energy transfer so that another competing rate constantk_(r)+k_(n) (=1/i) becomes relatively small.

<<Concept for Promoting Energy Transfer>>

First, energy transfer by Förster mechanism is considered. When Formula(1) is substituted into Formula (3), τ can be eliminated. Thus, inFörster mechanism, the energy transfer efficiency ϕ_(ET) does not dependon the lifetime t of the excited state of the high molecular material131. In addition, it can be said that the energy transfer efficiencyϕ_(ET) is higher when the luminescence quantum yield ϕ (here, thefluorescence quantum yield because energy transfer from a singletexcited state is discussed) is higher. In general, the luminescencequantum yield of an organic compound in a triplet excited state isextremely low at room temperature. Thus, in the case where the highmolecular material 131 is in a triplet excited state, a process ofenergy transfer by Förster mechanism can be ignored, and a process ofenergy transfer by Förster mechanism is considered only in the casewhere the high molecular material 131 is in a singlet excited state.

Furthermore, it is preferable that the emission spectrum (thefluorescent spectrum in the case where energy transfer from a singletexcited state is discussed) of the high molecular material 131 largelyoverlap with the absorption spectrum (absorption corresponding to thetransition from the singlet ground state to the singlet excited state)of the guest material 132. Moreover, it is preferable that the molarabsorption coefficient of the guest material 132 be also high. Thismeans that the emission spectrum of the high molecular material 131overlaps with the absorption band of the guest material 132 which is onthe longest wavelength side. Since direct transition from the singletground state to the triplet excited state of the guest material 132 isforbidden, the molar absorption coefficient of the guest material 132 inthe triplet excited state can be ignored. Thus, a process of energytransfer to a triplet excited state of the guest material 132 by Förstermechanism can be ignored, and only a process of energy transfer to asinglet excited state of the guest material 132 is considered. That is,in Förster mechanism, a process of energy transfer from the singletexcited state of the high molecular material 131 to the singlet excitedstate of the guest material 132 is considered.

Next, energy transfer by Dexter mechanism is considered. According toFormula (2), in order to increase the rate constant k_(h*→g), it ispreferable that an emission spectrum of the high molecular material 131(a fluorescent spectrum in the case where energy transfer from a singletexcited state is discussed) largely overlap with an absorption spectrumof the guest material 132 (absorption corresponding to transition from asinglet ground state to a singlet excited state). Therefore, the energytransfer efficiency can be optimized by making the emission spectrum ofthe high molecular material 131 overlap with the absorption band of theguest material 132 which is on the longest wavelength side.

When Formula (2) is substituted into Formula (3), it is found that theenergy transfer efficiency ϕ_(ET) in Dexter mechanism depends on τ. InDexter mechanism, which is a process of energy transfer based on theelectron exchange, as well as the energy transfer from the singletexcited state of the high molecular material 131 to the singlet excitedstate of the guest material 132, energy transfer from the tripletexcited state of the high molecular material 131 to the triplet excitedstate of the guest material 132 occurs.

In the light-emitting element of one embodiment of the present inventionin which the guest material 132 is a fluorescent compound, theefficiency of energy transfer to the triplet excited state of the guestmaterial 132 is preferably low. That is, the energy transfer efficiencybased on Dexter mechanism from the high molecular material 131 to theguest material 132 is preferably low and the energy transfer efficiencybased on Förster mechanism from the high molecular material 131 to theguest material 132 is preferably high.

As described above, the energy transfer efficiency in Förster mechanismdoes not depend on the lifetime τ of the excited state of the highmolecular material 131. In contrast, the energy transfer efficiency inDexter mechanism depends on the excitation lifetime t of the highmolecular material 131. Thus, to reduce the energy transfer efficiencyin Dexter mechanism, the excitation lifetime τ of the high molecularmaterial 131 is preferably short.

In a manner similar to that of the energy transfer from the highmolecular material 131 to the guest material 132, the energy transfer byboth Förster mechanism and Dexter mechanism also occurs in the energytransfer process from the excited complex to the guest material 132.

Accordingly, one embodiment of the present invention provides alight-emitting element including the high molecular material 131 inwhich two high molecular chains form an excited complex which functionsas an energy donor capable of efficiently transferring energy to theguest material 132. The excited complex formed by the two high molecularchains in the high molecular material 131 has a singlet excitationenergy level and a triplet excitation energy level which are close toeach other; accordingly, transition from a triplet exciton generated inthe light-emitting layer 130 to a singlet exciton (reverse intersystemcrossing) is likely to occur. This can increase the efficiency ofgenerating singlet excitons in the light-emitting layer 130.Furthermore, in order to facilitate energy transfer from the singletexcited state of the excited complex to the singlet excited state of theguest material 132 serving as an energy acceptor, it is preferable thatthe emission spectrum of the excited complex overlap with the absorptionband of the guest material 132 which is on the longest wavelength side(lowest energy side). Thus, the efficiency of generating the singletexcited state of the guest material 132 can be increased.

In addition, fluorescence lifetime of a thermally activated delayedfluorescence component in light emitted from the excited complex ispreferably short, and specifically, preferably 10 ns or longer and 50 μsor shorter, further preferably 10 ns or longer and 30 μs or shorter.

The proportion of a thermally activated delayed fluorescence componentin the light emitted from the excited complex is preferably high.Specifically, the proportion of a thermally activated delayedfluorescence component in the light emitted from the excited complex ispreferably higher than or equal to 5%, further preferably higher than orequal to 10%.

Structure Example 2 of Light-Emitting Element

Next, a structure example of the light-emitting layer 130 different fromthat in FIG. 1B is described below with reference to FIG. 2.

FIG. 2 is a schematic cross-sectional view illustrating another exampleof the light-emitting layer 130 in FIG. 1A. Note that in FIG. 2,portions having functions similar to those of portions in FIG. 1B aredenoted by the same reference numerals, and a detailed description ofthe portions is omitted in some cases.

The light-emitting layer 130 in FIG. 2 contains the high molecularmaterial 131. The high molecular material 131 includes the skeleton131_1, the skeleton 131_2, the skeleton 131_3, and a skeleton 131_4 asstructural units. The skeleton 131_1 and the skeleton 131_2 are bondedor polymerized to each other through the skeleton 131_3.

The skeleton 131_4 may be a light-emitting skeleton, and thelight-emitting skeleton is preferably a skeleton capable of emittingfluorescence (hereinafter also referred to as a fluorescent skeleton). Astructure in which a fluorescent skeleton is used as the skeleton 131_4will be described below. Note that the skeleton 131_4 may be rephrasedas the fluorescent skeleton.

The skeleton 131_4 has a function similar to that of the guest material132. Thus, this structure example can be described by rephrasing theguest material 132 shown in Structure example 1 of this embodiment asthe skeleton 131_4. In addition, Structure example 1 of this embodimentmay be referred to for the description of functions similar to those inStructure example 1 of this embodiment.

That is, in the light-emitting element of one embodiment of the presentinvention, the high molecular material 131 includes the skeleton havinga hole-transport property included in the skeleton 131_1 and theskeleton having an electron-transport property included in the skeleton131_2, and two high molecular chains form an excited complex. Then, theexcitation energy is transferred from the excited complex to theskeleton 131_4, whereby light is emitted from the skeleton 131_4. Notethat the skeleton 131_4 which receives the excitation energy from theexcited complex may be included in one of the two high molecular chainsforming the excited complex or may be included in another high molecularchain.

When the triplet excitation energy is transferred from the tripletexcitation energy level of the excited complex formed by the skeleton131_1 in one high molecular chain and the skeleton 131_2 in the otherhigh molecular chain to the triplet excitation energy level of theskeleton 1314, the triplet excitation energy is deactivated. Thus, thecomposition ratio of the skeleton 131_4 to all of the structural unitsof the high molecular material 131 is preferably low, specificallyhigher than or equal to 0.1 mol % and lower than or equal to 5 mol %,further preferably higher than or equal to 0.1 mol % and lower than orequal to 3 mol %, still further preferably higher than or equal to 0.1mol % and lower than or equal to 1 mol %.

When the direct carrier recombination process in the skeleton 131_4 isdominant, a large number of triplet excitons are generated in thelight-emitting layer 130, resulting in decreased light emissionefficiency due to thermal deactivation. Thus, as described above, thecomposition ratio of the skeleton 131_4 to all of the structural unitsof the high molecular material 131 is preferably low, specificallyhigher than or equal to 0.1 mol % and lower than or equal to 5 mol %,further preferably higher than or equal to 0.1 mol % and lower than orequal to 3 mol %, still further preferably higher than or equal to 0.1mol % and lower than or equal to 1 mol %.

<Material>

Next, components of a light-emitting element of one embodiment of thepresent invention are described in detail below.

<<Light-Emitting Layer>>

Next, materials that can be used for the light-emitting layer 130 willbe described below.

The high molecular material 131 in the light-emitting layer 130 is notparticularly limited as long as two high molecular chains of the highmolecular material 131 have a function of forming an excited complex;however, the high molecular material 131 preferably includes theπ-electron deficient heteroaromatic skeleton and at least one of theπ-electron rich heteroaromatic skeleton and the aromatic amine skeleton.That is, it is preferable that the high molecular material 131 includeat least the skeletons 131_1, 131_2, and 131_3, the skeleton 131_1include at least one of the π-electron rich heteroaromatic skeleton andthe aromatic amine skeleton, and the skeleton 131_2 include theπ-electron deficient heteroaromatic skeleton.

As the aromatic amine skeleton included in the high molecular material131, tertiary amine not including an NH bond, in particular, atriarylamine skeleton is preferably used. As an aryl group of atriarylamine skeleton, a substituted or unsubstituted aryl group having6 to 13 carbon atoms included in a ring is preferably used and examplesthereof include a phenyl group, a naphthyl group, and a fluorenyl group.

As the π-electron rich heteroaromatic skeleton included in the highmolecular material 131, one or more of a furan skeleton, a thiopheneskeleton, and a pyrrole skeleton are preferable because of their highstability and reliability. As a furan skeleton, a dibenzofuran skeletonis preferable. As a thiophene skeleton, a dibenzothiophene skeleton ispreferable. Note that as a pyrrole skeleton, an indole skeleton or acarbazole skeleton, in particular, a 3-(9H-carbazol-3-yl)-9H-carbazoleskeleton is preferable. Each of these skeletons may further have asubstituent.

As examples of the above-described aromatic amine skeleton andπ-electron rich heteroaromatic skeleton, skeletons represented by thefollowing general formulae (101) to (110) are given. Note that X in thegeneral formulae (105) to (107) represents an oxygen atom or a sulfuratom.

In addition, as the π-electron deficient heteroaromatic skeletonincluded in the second skeleton (the skeleton 131_2), a pyridineskeleton, a diazine skeleton (a pyrimidine skeleton, a pyrazineskeleton, or a pyridazine skeleton), or a triazine skeleton ispreferable; in particular, the diazine skeleton or the triazine skeletonis preferable because of its high stability and reliability.

As examples of the above-described π-electron deficient heteroaromaticskeleton, skeletons represented by the following general formulae (201)to (210) are given.

Note that as the second skeleton, instead of the above-describedπ-electron deficient heteroaromatic skeleton, an aromatic hydrocarbonskeleton whose triplet excitation energy is 2 eV or more, such as abiphenyl skeleton, a naphthalene skeleton, a phenanthrene skeleton, atriphenylene skeleton, or a fluorene skeleton may be used.

In addition, a skeleton having a hole-transport property included in thefirst skeleton (the skeleton 131_1) (specifically, at least one of theπ-electron rich heteroaromatic skeleton and the aromatic amine skeleton)and a skeleton having an electron-transport property included in thesecond skeleton (specifically, the π-electron deficient heteroaromaticskeleton) are preferably bonded or polymerized to each other through atleast the skeleton 131_3.

Examples of the skeleton 131_3 (the third skeleton) include a phenyleneskeleton, a biphenyldiyl skeleton, a terphenyldiyl skeleton, anaphthalenediyl skeleton, a fluorenediyl skeleton, a9,10-dihydroanthracenediyl skeleton, a phenanthrenediyl skeleton, and anarylenevinylene skeleton (a phenylenevinylene skeleton or the like),which are skeletons represented by the following general formulae (301)to (314), for example.

The above-described aromatic amine skeleton (e.g., the triarylamineskeleton), π-electron rich heteroaromatic skeleton (e.g., a ringincluding the furan skeleton, the thiophene skeleton, or the pyrroleskeleton), and π-electron deficient heteroaromatic skeleton (e.g., aring including the pyridine skeleton, the diazine skeleton, or thetriazine skeleton) or the above-described general formulae (101) to(110), general formulae (201) to (210), and general formulae (301) to(314) may each have a substituent. As the substituent, an alkyl group,an alkoxy group, or an alkylthio group having 1 to 20 carbon atoms, acycloalkyl group having 3 to 20 carbon atoms, a substituted orunsubstituted aryl group or aryloxy group having 6 to 18 carbon atoms,or a heterocyclic compound group having 4 to 14 carbon atoms can also beselected. Specific examples of the alkyl group having 1 to 20 carbonatoms include a methyl group, an ethyl group, a propyl group, anisopropyl group, a butyl group, an isobutyl group, a tert-butyl group, apentyl group, a hexyl group, a heptyl group, an octyl group, a decylgroup, a lauryl group, a 2-ethyl-hexyl group, a 3-methyl-butyl group,and the like. In addition, specific examples of the alkoxy group having1 to 20 carbon atoms include a methoxy group, an ethoxy group, a butoxygroup, a pentyloxy group, a hexyloxy group, a heptyloxy group, anoctyloxy group, a decyloxy group, a lauryloxy group, a 2-ethyl-hexyloxygroup, a 3-methyl-butoxy group, an isopropyloxy group, and the like. Inaddition, specific examples of the alkylthio group having 1 to 20 carbonatoms include a methylthio group, an ethylthio group, a butylthio group,a pentylthio group, a hexylthio group, a heptylthio group, an octylthiogroup, a decylthio group, a laurylthio group, a 2-ethyl-hexylthio group,a 3-methyl-butylthio group, an isopropylthio group, and the like.Specific examples of the cycloalkyl group having 3 to 20 carbon atomsinclude a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, acyclohexyl group, a norbomyl group, a noradamantyl group, an adamantylgroup, a homoadamantyl group, a tricyclodecanyl group, and the like.Specific examples of the aryl group having 6 to 18 carbon atoms includea substituted or unsubstituted phenyl group, naphthyl group, biphenylgroup, fluorenyl group, anthracenyl group, pyrenyl group, and the like.In addition, specific examples of an aryloxy group having 6 to 18 carbonatoms include a substituted or unsubstituted alkoxyphenoxy group,alkylphenoxy group, naphthyloxy group, anthracenyloxy group, pyrenyloxygroup, and the like. Specific examples of the heterocyclic compoundgroup having 4 to 14 carbon atoms include a substituted or unsubstitutedthienyl group, pyrrolyl group, furyl group, pyridyl group, and the like.The above substituents may be bonded to each other to form a ring. Forexample, in the case where a carbon atom at the 9-position in a fluoreneskeleton has two phenyl groups as substituents, the phenyl groups arebonded to form a spirofluorene skeleton. Note that an unsubstitutedgroup has an advantage in easy synthesis and an inexpensive rawmaterial.

Furthermore, Ar represents an arylene group having 6 to 18 carbon atoms.The arylene group may include one or more substituents and thesubstituents may be bonded to each other to form a ring. For example, acarbon atom at the 9-position in a fluorenyl group has two phenyl groupsas substituents and the phenyl groups are bonded to form a spirofluoreneskeleton. Specific examples of the arylene group having 6 to 18 carbonatoms include a phenylene group, a naphthylene group, a biphenyldiylgroup, a fluorenediyl group, an anthracenediyl group, a phenanthrenediylgroup, a pyrenediyl group, a perylenediyl group, a chrysenediyl group,an alkoxyphenylene group, and the like. In the case where the arylenegroup has a substituent, as the substituent, an alkyl group, an alkoxygroup, or an alkylthio group having 1 to 20 carbon atoms, a cycloalkylgroup having 3 to 20 carbon atoms, a substituted or unsubstituted arylgroup or aryloxy group having 6 to 18 carbon atoms, or a heterocycliccompound group having 4 to 14 carbon atoms can also be selected.Specific examples of the alkyl group having 1 to 20 carbon atoms includea methyl group, an ethyl group, a propyl group, an isopropyl group, abutyl group, an isobutyl group, a tert-butyl group, a pentyl group, ahexyl group, a heptyl group, an octyl group, a decyl group, a laurylgroup, a 2-ethyl-hexyl group, a 3-methyl-butyl group, and the like. Inaddition, specific examples of the alkoxy group having 1 to 20 carbonatoms include a methoxy group, an ethoxy group, a butoxy group, apentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group,a decyloxy group, a lauryloxy group, a 2-ethyl-hexyloxy group, a3-methyl-butoxy group, an isobutoxy group, and the like. In addition,specific examples of the alkylthio group having 1 to 20 carbon atomsinclude a methylthio group, an ethylthio group, a butylthio group, apentylthio group, a hexylthio group, a heptylthio group, an octylthiogroup, a decylthio group, a laurylthio group, a 2-ethyl-hexylthio group,a 3-methyl-butylthio group, an isopropylthio group, and the like.Specific examples of the cycloalkyl group having 3 to 20 carbon atomsinclude a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, acyclohexyl group, a norbomyl group, a noradamantyl group, an adamantylgroup, a homoadamantyl group, a tricyclodecanyl group, and the like.Specific examples of the aryl group having 6 to 18 carbon atoms includea substituted or unsubstituted phenyl group, naphthyl group, biphenylgroup, fluorenyl group, anthracenyl group, pyrenyl group, and the like.In addition, specific examples of an aryloxy group having 6 to 18 carbonatoms include a substituted or unsubstituted alkoxyphenoxy group,alkylphenoxy group, naphthyloxy group, anthracenyloxy group, pyrenyloxygroup, and the like. Specific examples of the heterocyclic compoundgroup having 4 to 14 carbon atoms include a substituted or unsubstitutedthienyl group, pyrrolyl group, furyl group, pyridyl group, and the like.

As the arylene group represented by Ar, for example, groups representedby the following structural formulae (Ar-1) to (Ar-18) can be used. Notethat the group that can be used as Ar is not limited to these.

Furthermore, R¹ and R² each independently represent any of hydrogen, analkyl group, an alkoxy group, or an alkylthio group having 1 to 20carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, asubstituted or unsubstituted aryl group or aryloxy group having 6 to 18carbon atoms, and a heterocyclic compound group having 4 to 14 carbonatoms. Specific examples of the alkyl group having 1 to 20 carbon atomsinclude a methyl group, an ethyl group, a propyl group, an isopropylgroup, a butyl group, an isobutyl group, a tert-butyl group, a pentylgroup, a hexyl group, a heptyl group, an octyl group, a decyl group, alauryl group, a 2-ethyl-hexyl group, a 3-methyl-butyl group, and thelike. In addition, specific examples of the alkoxy group having 1 to 20carbon atoms include a methoxy group, an ethoxy group, a butoxy group, apentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group,a decyloxy group, a lauryloxy group, a 2-ethyl-hexyloxy group, a3-methyl-butoxy group, an isobutoxy group, and the like. In addition,specific examples of the alkylthio group having 1 to 20 carbon atomsinclude a methylthio group, an ethylthio group, a butylthio group, apentylthio group, a hexylthio group, a heptylthio group, an octylthiogroup, a decylthio group, a laurylthio group, a 2-ethyl-hexylthio group,a 3-methyl-butylthio group, an isopropylthio group, and the like.Specific examples of the cycloalkyl group having 3 to 20 carbon atomsinclude a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, acyclohexyl group, a norbomyl group, a noradamantyl group, an adamantylgroup, a homoadamantyl group, a tricyclodecanyl group, and the like.Specific examples of the aryl group having 6 to 18 carbon atoms includea substituted or unsubstituted phenyl group, naphthyl group, biphenylgroup, fluorenyl group, anthracenyl group, pyrenyl group, and the like.In addition, specific examples of an aryloxy group having 6 to 18 carbonatoms include a substituted or unsubstituted alkoxyphenoxy group,alkylphenoxy group, naphthyloxy group, anthracenyloxy group, pyrenyloxygroup, and the like. Specific examples of the heterocyclic compoundgroup having 4 to 14 carbon atoms include a substituted or unsubstitutedthienyl group, pyrrolyl group, furyl group, pyridyl group, and the like.The above R¹ and R² may each have a substituent, and the substituentsmay be bonded to each other to form a ring. As the substituent, an alkylgroup, an alkoxy group, or an alkylthio group having 1 to 20 carbonatoms, a cycloalkyl group having 3 to 20 carbon atoms, a substituted orunsubstituted aryl group or aryloxy group having 6 to 18 carbon atoms,or a heterocyclic compound group having 4 to 14 carbon atoms can also beselected. Specific examples of the alkyl group having 1 to 20 carbonatoms include a methyl group, an ethyl group, a propyl group, anisopropyl group, a butyl group, an isobutyl group, a tert-butyl group, apentyl group, a hexyl group, a heptyl group, an octyl group, a decylgroup, a lauryl group, a 2-ethyl-hexyl group, a 3-methyl-butyl group,and the like. In addition, specific examples of the alkoxy group having1 to 20 carbon atoms include a methoxy group, an ethoxy group, a butoxygroup, a pentyloxy group, a hexyloxy group, a heptyloxy group, anoctyloxy group, a decyloxy group, a lauryloxy group, a 2-ethyl-hexyloxygroup, a 3-methyl-butoxy group, an isobutoxy group, and the like. Inaddition, specific examples of the alkylthio group having 1 to 20 carbonatoms include a methylthio group, an ethylthio group, a butylthio group,a pentylthio group, a hexylthio group, a heptylthio group, an octylthiogroup, a decylthio group, a laurylthio group, a 2-ethyl-hexylthio group,a 3-methyl-butylthio group, an isopropylthio group, and the like.Specific examples of the cycloalkyl group having 3 to 20 carbon atomsinclude a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, acyclohexyl group, a norbornyl group, a noradamantyl group, an adamantylgroup, a homoadamantyl group, a tricyclodecanyl group, and the like.Specific examples of the aryl group having 6 to 18 carbon atoms includea substituted or unsubstituted phenyl group, naphthyl group, biphenylgroup, fluorenyl group, anthracenyl group, pyrenyl group, and the like.In addition, specific examples of an aryloxy group having 6 to 18 carbonatoms include a substituted or unsubstituted alkoxyphenoxy group,alkylphenoxy group, naphthyloxy group, anthracenyloxy group, pyrenyloxygroup, and the like. Specific examples of the heterocyclic compoundgroup having 4 to 14 carbon atoms include a substituted or unsubstitutedthienyl group, pyrrolyl group, furyl group, pyridyl group, and the like.

For example, groups represented by the following structural formulae(R-1) to (R-29) can be used as the alkyl group or aryl group representedby R¹ and R² and the substituents which can be included in the generalformulae (101) to (110), the general formulae (201) to (210), thegeneral formulae (301) to (314), Ar, R¹, and R². Note that the groupswhich can be used as an alkyl group or an aryl group are not limitedthereto.

In the light-emitting layer 130, there is no particular limitation onthe guest material 132, but the guest material 132 is preferably ananthracene derivative, a tetracene derivative, a chrysene derivative, aphenanthrene derivative, a pyrene derivative, a perylene derivative, astilbene derivative, an acridone derivative, a coumarin derivative, aphenoxazine derivative, a phenothiazine derivative, or the like, and forexample, any of the following substituted or unsubstituted materials canbe used. As the substituent, any of the above-described substituents canbe used.

The examples include5,6-bis[4-(10-phenyl-9-anthryl)phenyl]-2,2′-bipyridine (abbreviation:PAP2BPy), 5,6-bis[4′-(10-phenyl-9-anthryl)biphenyl-4-yl]-2,2′-bipyridine(abbreviation: PAPP2BPy),N,N′-diphenyl-N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation: 1,6FLPAPm),N,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPm),N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-bis(4-tert-butylphenyl)pyrene-1,6-diamine(abbreviation: 1,6tBu-FLPAPm),N,N′-diphenyl-N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-3,8-dicyclohexylpyrene-1,6-diamine(abbreviation: ch-1,6FLPAPm),N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), perylene, 2,5,8,11-tetra(tert-butyl)perylene(abbreviation: TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),N,N′-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine](abbreviation: DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: 2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPPA),N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine(abbreviation: DBC1), coumarin 30,N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), N,N, 9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), coumarin 6, coumarin 545T,N,N′-diphenylquinacridone (abbreviation: DPQd), rubrene,2,8-di-tert-butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyltetracene(abbreviation: TBRb), Nile red,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile(abbreviation: DCM1),2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCM2),N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD),2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTI),2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTB), 2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile(abbreviation: BisDCM),2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: BisDCJTM), and5,10,15,20-tetraphenylbisbenzo[5,6]indeno[1,2,3-cd:1′,2′,3′-lm]perylene.

As described above, the energy transfer efficiency based on Dextermechanism from the high molecular material 131 to the guest material 132is preferably low. The rate constant of Dexter mechanism is inverselyproportional to the exponential function of the distance between the twomolecules. Thus, when the distance between the two molecules isapproximately 1 nm or less, Dexter mechanism is dominant, and when thedistance is approximately 1 nm or more, Förster mechanism is dominant.To reduce the energy transfer efficiency in Dexter mechanism, thedistance between the high molecular material 131 and the guest material132 is preferably large, and specifically, 0.7 nm or more, preferably0.9 nm or more, further preferably 1 nm or more. In view of the above,the guest material 132 preferably has a substituent that prevents theproximity to the high molecular material 131. The substituent ispreferably aliphatic hydrocarbon, further preferably an alkyl group,still further preferably a branched alkyl group. Specifically, the guestmaterial 132 preferably includes at least two alkyl groups each having 2or more carbon atoms. Alternatively, the guest material 132 preferablyincludes at least two branched alkyl groups each having 3 to 10 carbonatoms. Alternatively, the guest material 132 preferably includes atleast two cycloalkyl groups each having 3 to 10 carbon atoms.

Alternatively, the guest material 132 may be a high molecular compound,for example, a compound including a phenylene group, a naphthalenediylgroup, an anthracenediyl group, a phenanthrenediyl group, adihydrophenanthrenediyl group, a carbazoldiyl group, a phenoxazinediylgroup, a phenothiazinediyl group, a pyrenediyl group, or the like.

In the light-emitting layer 130, the skeleton 131_4 is not particularlylimited; however, the skeleton 131_4 preferably includes alight-emitting skeleton which is included in the guest material 132.That is, for example, a structure in which one or two hydrogen atoms areremoved from an aromatic ring of a skeleton of anthracene, tetracene,chrysene, phenanthrene, pyrene, perylene, stilbene, acridone, coumarin,phenoxazine, phenothiazine, or the like is preferably used as thestructural unit. As the light-emitting skeleton, any of the skeletonsrepresented by the following general formulae (401) to (410) from whichone or two hydrogen atoms are removed is used. In addition, each of theskeletons preferably includes a substituent. In order to suppress theabove-described Dexter transfer, an aliphatic hydrocarbon group,preferably an alkyl group, further preferably a branched alkyl group maybe introduced as the substituent. Specifically, the skeleton 131_4preferably includes at least two alkyl groups each having 2 or morecarbon atoms. Alternatively, the skeleton 131_4 preferably includes atleast two branched alkyl groups each having 3 to 10 carbon atoms.Alternatively, the skeleton 131_4 preferably includes at least twocycloalkyl groups each having 3 to 10 carbon atoms.

The light-emitting layer 130 may contain another material in addition tothe high molecular material 131 and the guest material 132. For example,a substituted or unsubstituted material of any of the followinghole-transport materials and electron-transport materials can be used.Note that as the substituent, any of the above-described substituentscan be used.

A material having a property of transporting more holes than electronscan be used as the hole-transport material, and a material having a holemobility of 1×10⁻⁶ cm²/Vs or higher is preferable. Specifically, anaromatic amine, a carbazole derivative, an aromatic hydrocarbon, astilbene derivative, or the like can be used. Furthermore, thehole-transport material may be a high molecular compound. Furthermore, ahigh molecular compound including the hole-transport skeleton, theπ-electron rich heteroaromatic skeleton, or the aromatic amine skeleton,which is included in the high molecular material 131 may be used.

Examples of the material having a high hole-transport property areN,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation:DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl(abbreviation: DPAB),N,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B), and the like.

Specific examples of the carbazole derivative are3-[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA1),3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA2),3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole(abbreviation: PCzTPN2),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1), and the like.

Other examples of the carbazole derivative are4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB),9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA),1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene, and thelike.

Examples of the aromatic hydrocarbon are2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, andthe like. Other examples are pentacene, coronene, and the like. Thearomatic hydrocarbon having a hole mobility of 1×10⁻⁶ cm²/Vs or higherand having 14 to 42 carbon atoms is particularly preferable.

The aromatic hydrocarbon may have a vinyl skeleton. Examples of thearomatic hydrocarbon having a vinyl group are4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi),9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA),and the like.

Other examples are high molecular compounds such aspoly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine)(abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:poly-TPD).

Examples of the material having a high hole-transport property arearomatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(carbazol-9-yl)triphenylamine(abbreviation: TCTA),4,4′,4″-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation:1′-TNATA), 4,4′,4″-tris(N,N′-diphenylamino)triphenylamine (abbreviation:TDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: mBPAFLP),N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N-phenyl-N-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine(abbreviation: DFLADFL),N-(9,9-dimethyl-2-diphenylamino-9H-fluoren-7-yl)diphenylamine(abbreviation: DPNF),2-[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPASF),4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBBi1BP),4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBANB),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),4-phenyldiphenyl-(9-phenyl-9H-carbazol-3-yl)amine (abbreviation:PCA1BP),N,N′-bis(9-phenylcarbazol-3-yl)-N,N′-diphenylbenzene-1,3-diamine(abbreviation: PCA2B),N,N,N′-triphenyl-N,N,N′-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine(abbreviation: PCA3B),N-(4-biphenyl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9-phenyl-9H-carbazol-3-amine(abbreviation: PCBiF),N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF),9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine(abbreviation: PCBAF),N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9′-bifluoren-2-amine(abbreviation: PCBASF),2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: PCASF),2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-spiro-9,9′-bifluorene(abbreviation: DPA2SF),N-[4-(9H-carbazol-9-yl)phenyl]-N-(4-phenyl)phenylaniline (abbreviation:YGA1BP), andN,N′-bis[4-(carbazol-9-yl)phenyl]-N,N′-diphenyl-9,9-dimethylfluorene-2,7-diamine(abbreviation: YGA2F). Other examples are amine compounds, carbazolecompounds, thiophene compounds, furan compounds, fluorene compounds;triphenylene compounds; phenanthrene compounds, and the like such as3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPN),3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation:PCPPn), 3,3′-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP),1,3-bis(N-carbazolyl)benzene (abbreviation: mCP),3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP),3,6-di(9H-carbazol-9-yl)-9-phenyl-9H-carbazole (abbreviation: PhCzGI),2,8-di(9H-carbazol-9-yl)-dibenzothiophene (abbreviation: Cz2DBT),4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran(abbreviation: mmDBFFLBi-II),4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II),1,3,5-tri(dibenzothiophen-4-yl)-benzene (abbreviated as DBT3P-II),2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene(abbreviation: DBTFLP-III),4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene(abbreviation: DBTFLP-IV), and4-[3-(triphenylene-2-yl)phenyl]dibenzothiophene (abbreviation:mDBTPTp-II). The substances described here are mainly substances havinga hole mobility of 1×10⁻⁶ cm²/Vs or higher. Note that other than thesesubstances, any substance that has a property of transporting more holesthan electrons may be used.

As the electron-transport material, a material having a property oftransporting more electrons than holes can be used, and a materialhaving an electron mobility of 1×10⁻⁶ cm²/Vs or higher is preferable. Aπ-electron deficient heteroaromatic compound such as anitrogen-containing heteroaromatic compound, a metal complex, or thelike can be used as the material which easily accepts electrons (thematerial having an electron-transport property). Specific examplesinclude a metal complex having a quinoline ligand, a benzoquinolineligand, an oxazole ligand, or a thiazole ligand, an oxadiazolederivative, a triazole derivative, a phenanthroline derivative, apyridine derivative, a bipyridine derivative, a pyrimidine derivative,and the like. Furthermore, the electron-transport material may be a highmolecular compound. Furthermore, a high molecular compound including theelectron-transport skeleton or the π-electron deficient heteroaromaticskeleton, which is included in the high molecular material 131 may beused.

Examples include metal complexes having a quinoline or benzoquinolineskeleton, such as tris(8-quinolinolato)aluminum(III) (abbreviation:Alq), tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation: Almq3),bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq2),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq) and bis(8-quinolinolato)zinc(II) (abbreviation:Znq), and the like. Alternatively, a metal complex having anoxazole-based or thiazole-based ligand, such asbis[2-(2-benzoxazolyl)phenolate]zinc(II) (abbreviation: ZnPBO) orbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ) can beused. Other than such metal complexes, any of the following can be used:heterocyclic compounds such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:COl), 3-(biphenyl-4-yl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),9-[4-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenyl]-9H-carbazole(abbreviation: CzTAZ1),2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI),2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II), bathophenanthroline (abbreviation: BPhen),and bathocuproine (abbreviation: BCP); heterocyclic compounds having adiazine skeleton such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III),7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II), 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 6mDBTPDBq-II),2-[3-(3,9′-bi-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzCzPDBq),4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation:4,6mPnP2Pm), 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine(abbreviation: 4,6mDBTP2Pm-II), and4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation:4,6mCzP2Pm); heterocyclic compounds having a triazine skeleton such as2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: PCCzPTzn); heterocyclic compounds having a pyridineskeleton such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine(abbreviation: 35DCzPPy); and heteroaromatic compounds such as4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs). Amongthe heterocyclic compounds, the heterocyclic compounds having diazineskeletons (pyrimidine, pyrazine, pyridazine) or having a pyridineskeleton are highly reliable and stable and is thus preferably used. Inaddition, the heterocyclic compounds having the skeletons have a highelectron-transport property to contribute to a reduction in drivingvoltage. Further alternatively, a high molecular compound such aspoly(2,5-pyridinediyl) (abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py), orpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can be used. The substances described here aremainly substances having an electron mobility of 1×10⁻⁶ cm²/Vs orhigher. Note that other substances may also be used as long as theirelectron-transport properties are higher than their hole-transportproperties.

In addition, the high molecular material 131 may have a structure whereone or two hydrogen atoms are removed from any of the above-describedhole-transport materials and electron-transport materials.

In addition, the light-emitting layer 130 may contain a thermallyactivated delayed fluorescent emitter in addition to the high molecularmaterial 131 and the guest material 132. Alternatively, a materialhaving a function of exhibiting thermally activated delayed fluorescenceat room temperature is preferably contained. Note that a thermallyactivated delayed fluorescent emitter is a material which can generate asinglet excited state from a triplet excited state by reverseintersystem crossing by thermal activation. The thermally activateddelayed fluorescent emitter may contain a material which can generate asinglet excited state by itself from a triplet excited state by reverseintersystem crossing, for example, a TADF material. Such a materialpreferably has a difference between the singlet excitation energy leveland the triplet excitation energy level of larger than 0 eV and smallerthan or equal to 0.2 eV.

As the TADF material serving as the thermally activated delayedfluorescent emitter, for example, any of the following materials can beused.

First, a fullerene, a derivative thereof, an acridine derivative such asproflavine, eosin, and the like can be given. Furthermore, ametal-containing porphyrin, such as a porphyrin containing magnesium(Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), orpalladium (Pd), can be given. Examples of the metal-containing porphyrininclude a protoporphyrin-tin fluoride complex (SnF₂(Proto IX)), amesoporphyrin-tin fluoride complex (SnF₂(Meso IX)), ahematoporphyrin-tin fluoride complex (SnF₂(Hemato IX)), a coproporphyrintetramethyl ester-tin fluoride complex (SnF₂(Copro III-4Me)), anoctaethylporphyrin-tin fluoride complex (SnF₂(OEP)), anetioporphyrin-tin fluoride complex (SnF₂(Etio I)), and anoctaethylporphyrin-platinum chloride complex (PtCl₂OEP).

As the thermally activated delayed fluorescence material composed of onekind of material, a heterocyclic compound having a π-electron richheteroaromatic ring and a π-electron deficient heteroaromatic ring canbe used. Specifically,2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine(abbreviation: PIC-TRZ),2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine(abbreviation: PCCzPTzn),2-[4-(10H-phenoxazin-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine(abbreviation: PXZ-TRZ),3-[4-(5-phenyl-5,10-dihydrophenazine-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole(abbreviation: PPZ-3TPT),3-(9,9-dimethyl-9H-acridin-10-yl)-9H-xanthen-9-one (abbreviation:ACRXTN), bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone(abbreviation: DMAC-DPS), or10-phenyl-10H,10′H-spiro[acridin-9,9′-anthracen]-10′-one (abbreviation:ACRSA), can be used. The heterocyclic compound is preferable because ofhaving the π-electron rich heteroaromatic ring and the π-electrondeficient heteroaromatic ring, for which the electron-transport propertyand the hole-transport property are high. Note that a substance in whichthe π-electron rich heteroaromatic ring is directly bonded to theπ-electron deficient heteroaromatic ring is particularly preferablebecause the donor property of the π-electron rich heteroaromatic ringand the acceptor property of the π-electron deficient heteroaromaticring are both increased and the difference between the singletexcitation energy level and the triplet excitation energy level becomessmall.

Alternatively, the thermally activated delayed fluorescent material maycontain a combination of two kinds of materials which form an excitedcomplex. As the combination of two kinds of materials, a combination ofthe above-described hole-transport material and electron-transportmaterial is preferable. Specifically, a zinc- or aluminum-based metalcomplex, an oxadiazole derivative, a triazole derivative, abenzimidazole derivative, a quinoxaline derivative, a dibenzoquinoxalinederivative, a dibenzothiophene derivative, a dibenzofuran derivative, apyrimidine derivative, a triazine derivative, a pyridine derivative, abipyridine derivative, a phenanthroline derivative, or the like can beused. Other examples are an aromatic amine and a carbazole derivative.

As the material that can be used for the light-emitting layer 130, amaterial capable of being dissolved in a solvent which can dissolve thehigh molecular material of one embodiment of the present invention ispreferable.

The light-emitting layer 130 can have a structure in which two or morelayers are stacked. For example, in the case where the light-emittinglayer 130 is formed by stacking a first light-emitting layer and asecond light-emitting layer in this order from the hole-transport layerside, the first light-emitting layer is formed using a substance havinga hole-transport property as the high molecular material and the secondlight-emitting layer is formed using a substance having anelectron-transport property as the high molecular material.

<<Hole-Injection Layer>>

The hole-injection layer 111 has a function of reducing a barrier forhole injection from one of the pair of electrodes (the electrode 101 orthe electrode 102) to promote hole injection and is formed using atransition metal oxide, a phthalocyanine derivative, or an aromaticamine, for example. As the transition metal oxide, molybdenum oxide,vanadium oxide, ruthenium oxide, tungsten oxide, manganese oxide, or thelike can be given. As the phthalocyanine derivative, phthalocyanine,metal phthalocyanine, or the like can be given. As the aromatic amine, abenzidine derivative, a phenylenediamine derivative, or the like can begiven. It is also possible to use a high molecular compound such aspolythiophene or polyaniline; a typical example thereof ispoly(ethylenedioxythiophene)/poly(styrenesulfonic acid), which isself-doped polythiophene. In addition, polyvinylcarbazole and aderivative thereof, polyarylene including an aromatic amine skeleton ora π-electron rich heteroaromatic skeleton in a side chain or a mainchain and a derivative thereof, and the like are given as examples.

As the hole-injection layer 111, a layer containing a composite materialof a hole-transport material and a material having a property ofaccepting electrons from the hole-transport material can also be used.Alternatively, a stack of a layer containing a material having anelectron accepting property and a layer containing a hole-transportmaterial may also be used. In a steady state or in the presence of anelectric field, electric charge can be transferred between thesematerials. As examples of the material having an electron-acceptingproperty, organic acceptors such as a quinodimethane derivative, achloranil derivative, and a hexaazatriphenylene derivative can be given.A specific example is a compound having an electron-withdrawing group (ahalogen group or a cyano group), such as7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F4-TCNQ), chloranil, or2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation:HAT-CN). Alternatively, a transition metal oxide such as an oxide of ametal from Group 4 to Group 8 can also be used. Specifically, vanadiumoxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, rhenium oxide, or the like can be used.In particular, molybdenum oxide is preferable because it is stable inthe air, has a low hygroscopic property, and is easily handled.

A material having a property of transporting more holes than electronscan be used as the hole-transport material, and a material having a holemobility of 1×10⁻⁶ cm²/Vs or higher is preferable. Specifically, any ofthe aromatic amine, carbazole derivative, aromatic hydrocarbon, stilbenederivative, and the like described as examples of the hole-transportmaterial that can be used in the light-emitting layer 130 can be used.Furthermore, the hole-transport material may be a high molecularcompound.

<<Hole-Transport Layer>>

A hole-transport layer may be provided between the hole-injection layer111 and the light-emitting layer 130. The hole-transport layer is alayer containing a hole-transport material and can be formed using anyof the hole-transport materials given as examples of the material of thehole-injection layer 111. In order that the hole-transport layer has afunction of transporting holes injected into the hole-injection layer111 to the light-emitting layer 130, the HOMO level of thehole-transport layer is preferably equal or close to the HOMO level ofthe hole-injection layer 111.

As the hole-transport material, a substance having a hole mobility of1×10⁻⁶ cm²/Vs or higher is preferably used. Note that any substanceother than the above substances may be used as long as thehole-transport property is higher than the electron-transport property.The layer including a substance having a high hole-transport property isnot limited to a single layer, and two or more layers containing theaforementioned substances may be stacked.

<<Electron-Transport Layer>>

An electron-transport layer may be provided between the light-emittinglayer 130 and the electron-injection layer 114. The electron-transportlayer has a function of transporting, to the light-emitting layer 130,electrons injected from the other of the pair of electrodes (theelectrode 101 or the electrode 102) through the electron-injection layer114. A material having a property of transporting more electrons thanholes can be used as the electron-transport material, and a materialhaving an electron mobility of 1×10⁻⁶ cm²/Vs or higher is preferable. Asthe compound which easily accepts electrons (the material having anelectron-transport property), a π-electron deficient heteroaromaticcompound such as a nitrogen-containing heteroaromatic compound, a metalcomplex, or the like can be used, for example. Specifically, a metalcomplex having a quinoline ligand, a benzoquinoline ligand, an oxazoleligand, or a thiazole ligand, an oxadiazole derivative; a triazolederivative, a phenanthroline derivative, a pyridine derivative, abipyridine derivative, a pyrimidine derivative, and the like, which aredescribed as the electron-transport materials that can be used in thelight-emitting layer 130, can be given. In addition, a high molecularcompound such as polyphenylene, polyfluorene, and derivatives thereofmay be used. A substance having an electron mobility of 1×10⁻⁶ cm²/Vs orhigher is preferable. Note that other than these substances, anysubstance that has a property of transporting more electrons than holesmay be used for the electron-transport layer. The electron-transportlayer is not limited to a single layer, and may include stacked two ormore layers containing the aforementioned substances.

Between the electron-transport layer and the light-emitting layer 130, alayer that controls transfer of electron carriers may be provided. Thisis a layer formed by addition of a small amount of a substance having ahigh electron-trapping property to a material having a highelectron-transport property described above, and the layer is capable ofadjusting carrier balance by suppressing transfer of electron carriers.Such a structure is very effective in preventing a problem (such as areduction in element lifetime) caused when electrons pass through thelight-emitting layer.

<<Electron-Injection Layer>>

The electron-injection layer 114 has a function of reducing a barrierfor electron injection from the electrode 102 to promote electroninjection and can be formed using a Group 1 metal or a Group 2 metal, oran oxide, a halide, or a carbonate of any of the metals, for example.Alternatively, a composite material containing an electron-transportmaterial (described above) and a material having a property of donatingelectrons to the electron-transport material can also be used. As thematerial having an electron-donating property, a Group 1 metal, a Group2 metal, an oxide of any of the metals, or the like can be given.Specifically, an alkali metal, an alkaline earth metal, or a compoundthereof, such as lithium fluoride (LiF), sodium fluoride (NaF), cesiumfluoride (CsF), calcium fluoride (CaF₂), or lithium oxide (LiOx), can beused. Alternatively, a rare earth metal compound like erbium fluoride(ErF₃) can be used. Electride may also be used for theelectron-injection layer 114. Examples of the electride include asubstance in which electrons are added at high concentration to calciumoxide-aluminum oxide. The electron-injection layer 114 can be formedusing the substance that can be used for the electron-transport layer118.

A composite material in which an organic compound and an electron donor(donor) are mixed may also be used for the electron-injection layer 114.Such a composite material is excellent in an electron-injection propertyand an electron-transport property because electrons are generated inthe organic compound by the electron donor. In this case, the organiccompound is preferably a material that is excellent in transporting thegenerated electrons. Specifically, the above-listed substances forforming the electron-transport layer (e.g., the metal complexes andheteroaromatic compounds) can be used, for example. As the electrondonor, a substance showing an electron-donating property with respect tothe organic compound may be used. Specifically, an alkali metal, analkaline earth metal, and a rare earth metal are preferable, andlithium, cesium, magnesium, calcium, erbium, and ytterbium are given. Inaddition, an alkali metal oxide or an alkaline earth metal oxide ispreferable, and lithium oxide, calcium oxide, barium oxide, and the likeare given. A Lewis base such as magnesium oxide can also be used. Anorganic compound such as tetrathiafulvalene (abbreviation: TTF) can alsobe used.

Note that the light-emitting layer, the hole-injection layer, thehole-transport layer, the electron-transport layer, and theelectron-injection layer described above can each be formed by anevaporation method (including a vacuum evaporation method), an inkjetmethod, a coating method, a nozzle-printing method, a gravure printingmethod, or the like. Besides the above-mentioned materials, an inorganiccompound such as a quantum dot may be used in the light-emitting layer,the hole-injection layer, the hole-transport layer, theelectron-transport layer, and the electron-injection layer.

The quantum dot may be a colloidal quantum dot, an alloyed quantum dot,a core-shell quantum dot, or a core quantum dot, for example. Thequantum dot containing elements belonging to Groups 2 and 16, elementsbelonging to Groups 13 and 15, elements belonging to Groups 13 and 17,elements belonging to Groups 11 and 17, or elements belonging to Groups14 and 15 may be used. Alternatively, the quantum dot containing anelement such as cadmium (Cd), selenium (Se), zinc (Zn), sulfur (S),phosphorus (P), indium (In), tellurium (Te), lead (Pb), gallium (Ga),arsenic (As), or aluminum (Al) may be used.

Examples of a solvent which can be used in the case where the inkjetmethod, the coating method, the nozzle-printing method, the gravureprinting method, or the like is used include: chlorine-based solventssuch as dichloroethane, trichloroethane, chlorobenzene, anddichlorobenzene; ether-based solvents such as tetrahydrofuran, dioxane,anisole, and methylanisole; aromatic hydrocarbon-based solvents such astoluene, xylene, mesitylene, ethylbenzene, hexylbenzene, andcyclohexylbenzene; aliphatic hydrocarbon-based solvents such ascyclohexane, methylcyclohexane, pentane, hexane, heptane, octane,nonane, decane, dodecane, and bicyclohexyl; ketone-based solvents suchas acetone, methyl ethyl ketone, benzophenone, and acetophenone;ester-based solvents such as ethyl acetate, butyl acetate, ethylcellosolve acetate, methyl benzoate, and phenyl acetate;polyalcohol-based solvents such as ethylene glycol, glycerin, andhexanediol; alcohol-based solvents such as isopropyl alcohol andcyclohexanol; a sulfoxide-based solvent such as dimethylsulfoxide; andamide-based solvents such as methylpyrrolidone and dimethylformamide. Asthe solvent, one or more materials can be used.

<<Pair of Electrodes>>

The electrodes 101 and 102 function as an anode and a cathode of eachlight-emitting element. The electrodes 101 and 102 can be formed using ametal, an alloy, or a conductive compound, a mixture or a stack thereof,or the like.

One of the electrode 101 and the electrode 102 is preferably formedusing a conductive material having a function of reflecting light.Examples of the conductive material include aluminum (Al), an alloycontaining Al, and the like. Examples of the alloy containing Al includean alloy containing Al and L (L represents one or more of titanium (Ti),neodymium (Nd), nickel (Ni), and lanthanum (La)), such as an alloycontaining Al and Ti and an alloy containing Al, Ni, and La. Aluminumhas low resistance and high light reflectivity. Aluminum is included inearth's crust in large amount and is inexpensive; therefore, it ispossible to reduce costs for manufacturing a light-emitting element withaluminum. Alternatively, Ag, an alloy of silver (Ag) and N (N representsone or more of yttrium (Y), Nd, magnesium (Mg), ytterbium (Yb), Al, Ti,gallium (Ga), zinc (Zn), indium (In), tungsten (W), manganese (Mn), tin(Sn), iron (Fe), Ni, copper (Cu), palladium (Pd), iridium (Ir), or gold(Au)), or the like can be used. Examples of the alloy containing silverinclude an alloy containing silver, palladium, and copper, an alloycontaining silver and copper, an alloy containing silver and magnesium,an alloy containing silver and nickel, an alloy containing silver andgold, an alloy containing silver and ytterbium, and the like. Besides, atransition metal such as tungsten, chromium (Cr), molybdenum (Mo),copper, or titanium can be used.

Light emitted from the light-emitting layer is extracted through theelectrode 101 and/or the electrode 102. Thus, at least one of theelectrode 101 and the electrode 102 is preferably formed using aconductive material having a function of transmitting light. As theconductive material, a conductive material having a visible lighttransmittance higher than or equal to 40% and lower than or equal to100%, preferably higher than or equal to 60% and lower than or equal to100%, and a resistivity lower than or equal to 1×10⁻² Ω·cm can be used.

The electrodes 101 and 102 may each be formed using a conductivematerial having functions of transmitting light and reflecting light. Asthe conductive material, a conductive material having a visible lightreflectivity higher than or equal to 20% and lower than or equal to 80%,preferably higher than or equal to 40% and lower than or equal to 70%,and a resistivity lower than or equal to 1×10⁻² Ω·cm can be used. Forexample, one or more kinds of conductive metals and alloys, conductivecompounds, and the like can be used. Specifically, a metal oxide such asindium tin oxide (hereinafter, referred to as ITO), indium tin oxidecontaining silicon or silicon oxide (ITSO), indium oxide-zinc oxide(indium zinc oxide), indium oxide-tin oxide containing titanium, indiumtitanium oxide, or indium oxide containing tungsten oxide and zinc oxidecan be used. A metal thin film having a thickness that allowstransmission of light (preferably, a thickness greater than or equal to1 nm and less than or equal to 30 nm) can also be used. As the metal,Ag, an alloy of Ag and Al, an alloy of Ag and Mg, an alloy of Ag and Au,an alloy of Ag and ytterbium (Yb), or the like can be used.

In this specification and the like, as the material transmitting light,a material that transmits visible light and has conductivity is used.Examples of the material include, in addition to the above-describedoxide conductor typified by an ITO, an oxide semiconductor and anorganic conductor containing an organic substance. Examples of theorganic conductive containing an organic substance include a compositematerial in which an organic compound and an electron donor (donormaterial) are mixed and a composite material in which an organiccompound and an electron acceptor (acceptor material) are mixed.Alternatively, an inorganic carbon-based material such as graphene maybe used. The resistivity of the material is preferably lower than orequal to 1×10⁵ Ω·cm, further preferably lower than or equal to 1×10⁴Ω·cm.

Alternatively, the electrode 101 and/or the electrode 102 may be formedby stacking two or more of these materials.

Furthermore, to increase light extraction efficiency, a material havinga higher refractive index than an electrode that has a function oftransmitting light may be formed in contact with the electrode. Such amaterial may be a conductive material or a non-conductive material aslong as having a function of transmitting visible light. For example, inaddition to the above-described oxide conductor, an oxide semiconductorand an organic material are given as examples. As examples of theorganic material, materials of the light-emitting layer, thehole-injection layer, the hole-transport layer, the electron-transportlayer, and the electron-injection layer are given. Alternatively, aninorganic carbon-based material or a metal thin film that allowstransmission of light can be used. A plurality of layers each of whichis formed using the material having a high refractive index and has athickness of several nanometers to several tens of nanometers may bestacked.

In the case where the electrode 101 or the electrode 102 functions asthe cathode, the electrode preferably contains a material having a lowwork function (lower than or equal to 3.8 eV). The examples include anelement belonging to Group 1 or 2 of the periodic table (e.g., an alkalimetal such as lithium, sodium, or cesium, an alkaline earth metal suchas calcium or strontium, or magnesium), an alloy containing any of theseelements (e.g., Ag—Mg or Al—Li), a rare earth metal such as europium(Eu) or Yb, an alloy containing any of these rare earth metals, an alloycontaining aluminum and silver, and the like.

In the case where the electrode 101 or the electrode 102 is used as ananode, a material having a high work function (higher than or equal to4.0 eV) is preferably used.

Alternatively, the electrodes 101 and 102 may each be a stack of aconductive material having a function of reflecting light and aconductive material having a function of transmitting light. In thatcase, the electrodes 101 and 102 can each have a function of adjustingthe optical path length so that light at a desired wavelength emittedfrom each light-emitting layer resonates and is intensified; thus, sucha structure is preferable.

As the method for forming the electrode 101 and the electrode 102, asputtering method, an evaporation method, a printing method, a coatingmethod, a molecular beam epitaxy (MBE) method, a CVD method, a pulsedlaser deposition method, an atomic layer deposition (ALD) method, or thelike can be used as appropriate.

<<Substrate>>

A light-emitting element in one embodiment of the present invention maybe formed over a substrate of glass, plastic, or the like. As the way ofstacking layers over the substrate, layers may be sequentially stackedfrom the electrode 101 side or sequentially stacked from the electrode102 side.

For the substrate over which the light-emitting element of oneembodiment of the present invention can be formed, glass, quartz,plastic, or the like can be used, for example. Alternatively, a flexiblesubstrate can be used. The flexible substrate means a substrate that canbe bent, such as a plastic substrate made of polycarbonate orpolyarylate, for example. Alternatively, a film, an inorganic vapordeposition film, or the like can be used. Another material may be usedas long as the substrate functions as a support in a manufacturingprocess of the light-emitting element or an optical element or as longas it has a function of protecting the light-emitting element or anoptical element.

In this specification and the like, a light-emitting element can beformed using any of a variety of substrates, for example. There is noparticular limitation on the type of substrate. Examples of thesubstrate include a semiconductor substrate (e.g., a single crystalsubstrate or a silicon substrate), an SOI substrate, a glass substrate,a quartz substrate, a plastic substrate, a metal substrate, a stainlesssteel substrate, a substrate including stainless steel foil, a tungstensubstrate, a substrate including tungsten foil, a flexible substrate, anattachment film, cellulose nanofiber (CNF) and paper which include afibrous material, a base material film, and the like. As an example of aglass substrate, a barium borosilicate glass substrate, analuminoborosilicate glass substrate, a soda lime glass substrate, andthe like can be given. Examples of the flexible substrate, theattachment film, the base material film, and the like are substrates ofplastics typified by polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polyether sulfone (PES), and polytetrafluoroethylene(PTFE). Another example is a resin such as acrylic. Furthermore,polypropylene, polyester, polyvinyl fluoride, and polyvinyl chloride canbe given as examples. Other examples are polyamide, polyimide, aramid,epoxy, an inorganic vapor deposition film, paper, and the like.

Alternatively, a flexible substrate may be used as the substrate suchthat the light-emitting element is provided directly on the flexiblesubstrate. Further alternatively, a separation layer may be providedbetween the substrate and the light-emitting element. The separationlayer can be used when part or the whole of a light-emitting elementformed over the separation layer is separated from the substrate andtransferred onto another substrate. In such a case, the light-emittingelement can be transferred to a substrate having low heat resistance ora flexible substrate as well. For the above separation layer, a stackincluding inorganic films, which are a tungsten film and a silicon oxidefilm, and a structure in which a resin film of polyimide or the like isformed over a substrate can be used, for example.

In other words, after the light-emitting element is formed using asubstrate, the light-emitting element may be transferred to anothersubstrate. Example of the substrate to which the light-emitting elementis transferred are, in addition to the above substrates, a cellophanesubstrate, a stone substrate, a wood substrate, a cloth substrate(including a natural fiber (e.g., silk, cotton, and hemp), a syntheticfiber (e.g., nylon, polyurethane, and polyester), a regenerated fiber(e.g., acetate, cupra, rayon, and regenerated polyester), and the like),a leather substrate, a rubber substrate, and the like. When such asubstrate is used, a light-emitting element with high durability, highheat resistance, reduced weight, or reduced thickness can be formed.

The light-emitting element 150 may be formed over an electrodeelectrically connected to a field-effect transistor (FET), for example,which is formed over any of the above-described substrates. Accordingly,an active matrix display device in which the FET controls the driving ofthe light-emitting element 150 can be manufactured.

In Embodiment 1, one embodiment of the present invention has beendescribed. Other embodiments of the present invention are described inEmbodiments 2 to 9. Note that one embodiment of the present invention isnot limited thereto. That is, since various embodiments of the presentinvention are disclosed in Embodiment 1 and Embodiments 2 to 9, oneembodiment of the present invention is not limited to a specificembodiment. The example in which one embodiment of the present inventionis used in a light-emitting element is described; however, oneembodiment of the present invention is not limited thereto. For example,depending on circumstances or conditions, one embodiment of the presentinvention is not necessarily used in a light-emitting element. Althoughanother example in which the EL layer includes the high molecularmaterial and the guest material, the high molecular material has astructure where the first skeleton and the second skeleton are bonded toeach other through the third skeleton, and the first high molecularchain and the second high molecular chain of the high molecular materialform an excited complex is shown as one embodiment of the presentinvention, one embodiment of the present invention is not limitedthereto. Depending on circumstances or conditions, the first highmolecular chain and the second high molecular chain of the highmolecular material do not need to form an excited complex in oneembodiment of the present invention, for example. Alternatively, thestructure where the first skeleton and the second skeleton in the highmolecular material are bonded to each other through the third skeletonis not necessarily provided. Although another example in which the firstskeleton in the high molecular material includes at least one of theπ-electron rich heteroaromatic skeleton and the aromatic amine skeletonand the second skeleton includes the π-electron deficient heteroaromaticskeleton is shown as one embodiment of the present invention, oneembodiment of the present invention is not limited thereto. Depending oncircumstances or conditions, the first skeleton does not necessarilyinclude the π-electron rich heteroaromatic skeleton or the aromaticamine skeleton in one embodiment of the present invention, for example.Alternatively, the second skeleton does not necessarily include theπ-electron deficient heteroaromatic skeleton.

The structures described in this embodiment can be used in appropriatecombination with any of the other embodiments.

Embodiment 2

In this embodiment, a light-emitting element having a structuredifferent from that described in Embodiment 1 and light emissionmechanisms of the light-emitting element are described below withreference to FIGS. 3A to 3C and FIG. 4. In FIG. 3A, a portion having afunction similar to that in FIG. 1A is represented by the same hatchpattern as in FIG. 1A and not especially denoted by a reference numeralin some cases. In addition, common reference numerals are used forportions having similar functions, and a detailed description of theportions is omitted in some cases.

Structure Example 1 of Light-Emitting Element

FIG. 3A is a schematic cross-sectional view of a light-emitting element152 of one embodiment of the present invention.

The light-emitting element 152 includes a pair of electrodes (anelectrode 101 and an electrode 102) and an EL layer 100 between the pairof electrodes. The EL layer 100 includes at least a light-emitting layer140.

Note that the electrode 101 functions as an anode and the electrode 102functions as a cathode in the following description of thelight-emitting element 152; however, the functions may be interchangedin the light-emitting element 152.

FIG. 3B is a schematic cross-sectional view illustrating an example ofthe light-emitting layer 140 in FIG. 3A. The light-emitting layer 140 inFIG. 3B includes a high molecular material 141 and a guest material 142.

The high molecular material 141 includes a skeleton 1411, a skeleton141_2, and a skeleton 141_3 as structural units. The skeleton 141_1 andthe skeleton 141_2 are bonded or polymerized to each other through theskeleton 141_3.

The guest material 142 may be a light-emitting organic compound, and thelight-emitting organic compound is preferably a substance capable ofemitting phosphorescence (hereinafter also referred to as aphosphorescent compound). A structure in which a phosphorescent compoundis used as the guest material 142 will be described below. The guestmaterial 142 may be rephrased as the phosphorescent compound.

<Light Emission Mechanism of Light-Emitting Element>

Next, the light emission mechanism of the light-emitting layer 140 isdescribed below.

In the high molecular material 141 in the light-emitting layer 140, itis preferable that the skeleton 141_1 include a skeleton having afunction of transporting holes (a hole-transport property) and theskeleton 141_2 include a skeleton having a function of transportingelectrons (an electron-transport property). Alternatively, it ispreferable that the skeleton 141_1 include at least one of a π-electronrich heteroaromatic skeleton and an aromatic amine skeleton and theskeleton 141_2 include a π-electron deficient heteroaromatic skeleton.

In one embodiment of the present invention, the high molecular material141 has a function of forming an excited complex (also referred to as anexcited dimer) with two high molecular chains of the high molecularmaterial 141. In particular, the skeleton having a hole-transportproperty and the skeleton having an electron-transport property of thehigh molecular material 141 preferably form an excited complex in twohigh molecular chains including the same structural units.Alternatively, at least one of the π-electron rich heteroaromaticskeleton and the aromatic amine skeleton included in the high molecularmaterial 141 and the π-electron deficient heteroaromatic skeletonincluded in the high molecular material 141 preferably form an excitedcomplex in two high molecular chains including the same structuralunits.

In other words, the high molecular material 141 has a function offorming an excited complex with a first high molecular chain and asecond high molecular chain of the high molecular material 141. Inparticular, the skeleton having a hole-transport property in the firsthigh molecular chain and the skeleton having an electron-transportproperty in the second high molecular chain of the high molecularmaterial 141 preferably form an excited complex. Alternatively, at leastone of the π-electron rich heteroaromatic skeleton and the aromaticamine skeleton in the first high molecular chain of the high molecularmaterial 141 and the π-electron deficient heteroaromatic skeleton in thesecond high molecular chain of the high molecular material 141preferably form an excited complex.

In the case where the high molecular material 141 includes the skeletonhaving a hole-transport property included in the skeleton 141_1 and theskeleton having an electron-transport property included in the skeleton1412, a donor-acceptor excited complex is easily formed by two highmolecular chains; thus, efficient formation of an excited complex ispossible. Alternatively, in the case where the high molecular material141 includes at least one of the π-electron rich heteroaromatic skeletonand the aromatic amine skeleton included in the skeleton 1411, and theπ-electron deficient heteroaromatic skeleton included in the skeleton141_2, a donor-acceptor excited complex is easily formed by two highmolecular chains; thus, efficient formation of an excited complex ispossible.

Thus, to increase both the donor property and the acceptor property inthe high molecular chains of the high molecular material 141, astructure where the conjugation between the skeleton having ahole-transport property and the skeleton having an electron-transportproperty is reduced is preferably used. Alternatively, a structure wherethe conjugation between the π-electron deficient heteroaromatic skeletonand at least one of the π-electron rich heteroaromatic skeleton and thearomatic amine skeleton is reduced is preferably used. Thus, adifference between a singlet excitation energy level and a tripletexcitation energy level of the high molecular material 141 can bereduced. Moreover, the triplet excitation energy level of the highmolecular material 141 can be high.

Furthermore, in the excited complex formed by the two high molecularchains including the same structural units, one high molecular chainincludes the HOMO and the other high molecular chain includes the LUMO;thus, an overlap between the HOMO and the LUMO is extremely small. Thatis, in the excited complex, a difference between a singlet excitationenergy level and a triplet excitation energy level is small. Therefore,in the excited complex formed by the two high molecular chains of thehigh molecular material 141, a difference between a singlet excitationenergy level and a triplet excitation energy level is small and ispreferably larger than 0 eV and smaller than or equal to 0.2 eV.

In the case where the high molecular material 141 includes the skeletonhaving a hole-transport property and the skeleton having anelectron-transport property, the carrier balance can be easilycontrolled. As a result, a carrier recombination region can also becontrolled easily. In order to achieve this, it is preferable that thecomposition ratio of the skeleton 141_1 (including the skeleton having ahole-transport property) to the skeleton 141_2 (including the skeletonhaving an electron-transport property) be in the range of 1:9 to 9:1(molar ratio), and it is further preferable that the proportion of theskeleton 141_2 (including the skeleton having an electron-transportproperty) be higher than the proportion of the skeleton 141_1 (includingthe skeleton having a hole-transport property).

FIG. 3C shows a correlation of energy levels of the high molecularmaterial 141 and the guest material 142 in the light-emitting layer 140.The following explains what terms and signs in FIG. 3C represent:

Polymer (141_1+141_2): the skeleton 141_1 in the first high molecularchain and the skeleton 141_2 in the second high molecular chain, whichare close to each other, of the high molecular material 141;

Guest (142): the guest material 142 (the phosphorescent compound);

S_(PH): the S1 level of the high molecular material 141;

T_(PH): the T1 level of the high molecular material 141;

T_(PG): the T1 level of the guest material 142 (the phosphorescentcompound);

S_(PE): the S1 level of the excited complex; and

T_(PE): the T1 level of the excited complex.

In the light-emitting layer 140, the high molecular material 141 ispresent in the largest proportion by weight, and the guest material 142(the phosphorescent compound) is dispersed in the high molecularmaterial 141. The T1 level of the high molecular material 141 in thelight-emitting layer 140 is preferably higher than the T1 level of theguest material (the guest material 142) in the light-emitting layer 140.

In the light-emitting element of one embodiment of the presentinvention, an excited complex is formed by the two high molecular chainsof the high molecular material 141 included in the light-emitting layer140. The lowest energy level (S_(PE)) in a singlet excited state of theexcited complex and the lowest energy level (T_(PE)) in a tripletexcited state of the excited complex are close to each other (see RouteE₇ in FIG. 3C).

In the two high molecular chains close to each other of the highmolecular material 141, one high molecular chain receives a hole and theother high molecular chain receives an electron to immediately form anexcited complex. Alternatively, one high molecular chain brought into anexcited state immediately interacts with the other high molecular chainto form an excited complex. Therefore, most excitons in thelight-emitting layer 140 exist as excited complexes. Because theexcitation energy levels (S_(PE) and T_(PE)) of the excited complex arelower than the singlet excitation energy level (S_(PH)) of the highmolecular material 141 that forms the excited complex, the excited stateof the high molecular material 141 can be formed with lower excitationenergy. Accordingly, the driving voltage of the light-emitting element152 can be reduced.

Both energies of S_(PE) and T_(PE) of the excited complex are thentransferred to the lowest energy level in the triplet excited state ofthe guest material 142 (the phosphorescent compound); thus, lightemission is obtained (see Routes E₅ and E₉ in FIG. 3C).

Furthermore, the triplet excitation energy level (T_(PE)) of the excitedcomplex is preferably higher than the triplet excitation energy level(T_(PG)) of the guest material 142. In this way, the singlet excitationenergy and the triplet excitation energy of the formed excited complexcan be transferred from the singlet excitation energy level (S_(PE)) andthe triplet excitation energy level (T_(PE)) of the excited complex tothe triplet excitation energy level (T_(PG)) of the guest material 142.

When the light-emitting layer 140 has the above-described structure,light emission from the guest material 142 (the phosphorescent compound)of the light-emitting layer 140 can be obtained efficiently.

Since an excited complex is called “an exciplex” in some cases, theabove-described processes through Routes E₇, E₈, and E₉ may be referredto as exciplex-triplet energy transfer (ExTET) in this specification andthe like. In other words, in the light-emitting layer 140, excitationenergy is transferred from the excited complex to the guest material142. In this case, the efficiency of reverse intersystem crossing fromT_(PE) to S_(PE) and the luminescence quantum yield from the singletexcited state having energy of S_(PE) are not necessarily high; thus,materials can be selected from a wide range of options.

Note that in order to efficiently transfer excitation energy from theexcited complex to the guest material 142, the triplet excitation energylevel (T_(PE)) of the excited complex formed by two high molecularchains is preferably lower than the triplet excitation energy level(T_(PH)) of the single high molecular material 141 which forms theexcited complex. Thus, quenching of the triplet excitation energy of theexcited complex due to another one or more high molecular chains in thehigh molecular material 141 is less likely to occur, which causesefficient energy transfer to the guest material 142.

Furthermore, the mechanism of the energy transfer process between themolecules of the high molecular material 141 and the guest material 142can be described using two mechanisms, i.e., Förster mechanism(dipole-dipole interaction) and Dexter mechanism (electron exchangeinteraction), as in Embodiment 1. For Förster mechanism and Dextermechanism, Embodiment 1 can be referred to.

<<Concept for Promoting Energy Transfer>>

In energy transfer by Förster mechanism, the energy transfer efficiency(ET is higher when the luminescence quantum yield ϕ (the fluorescencequantum yield when energy transfer from a singlet excited state isdiscussed) is higher. Furthermore, it is preferable that the emissionspectrum (the fluorescent spectrum in the case where energy transferfrom a singlet excited state is discussed) of the high molecularmaterial 141 largely overlap with the absorption spectrum (absorptioncorresponding to the transition from the singlet ground state to thetriplet excited state) of the guest material 142. Moreover, it ispreferable that the molar absorption coefficient of the guest material142 be also high. This means that the emission spectrum of the highmolecular material 141 overlaps with the absorption band of the guestmaterial 142 which is on the longest wavelength side.

In energy transfer by Dexter mechanism, in order to increase the rateconstant k_(h*→g), it is preferable that an emission spectrum of thehigh molecular material 141 (a fluorescent spectrum in the case whereenergy transfer from a singlet excited state is discussed) largelyoverlap with an absorption spectrum of the guest material 142(absorption corresponding to transition from a singlet ground state to atriplet excited state). Therefore, the energy transfer efficiency can beoptimized by making the emission spectrum of the high molecular material141 overlap with the absorption band of the guest material 142 which ison the longest wavelength side.

In a manner similar to that of the energy transfer from the highmolecular material 141 to the guest material 142, the energy transfer byboth Förster mechanism and Dexter mechanism also occurs in the energytransfer process from the excited complex to the guest material 142.

Accordingly, one embodiment of the present invention provides alight-emitting element including the high molecular material 141 inwhich two high molecular chains form an excited complex which functionsas an energy donor capable of efficiently transferring energy to theguest material 142. The excited complex formed by the two high molecularchains of the high molecular material 141 has a singlet excitationenergy level and a triplet excitation energy level which are close toeach other; accordingly, the excited complex generated in thelight-emitting layer 140 can be formed with lower excitation energy thanthe high molecular material 141 alone. This can reduce the drivingvoltage of the light-emitting element 152. Furthermore, in order tofacilitate energy transfer from the singlet excited state of the excitedcomplex to the triplet excited state of the guest material 142 servingas an energy acceptor, it is preferable that the emission spectrum ofthe excited complex overlap with the absorption band of the guestmaterial 142 which is on the longest wavelength side (lowest energyside). Thus, the efficiency of generating the triplet excited state ofthe guest material 142 can be increased.

Structure Example 2 of Light-Emitting Element

Next, a structure example of the light-emitting layer 140 different fromthat in FIG. 3B is described below with reference to FIG. 4.

FIG. 4 is a schematic cross-sectional view illustrating another exampleof the light-emitting layer 140 in FIG. 3A. Note that in FIG. 4,portions having functions similar to those of portions in FIG. 3B aredenoted by the same reference numerals, and a detailed description ofthe portions is omitted in some cases.

The light-emitting layer 140 in FIG. 4 contains the high molecularmaterial 141. The high molecular material 141 includes the skeleton141_1, the skeleton 1412, the skeleton 1413, and a skeleton 141_4 asstructural units. The skeleton 141_1 and the skeleton 141_2 are bondedor polymerized to each other through the skeleton 141_3.

The skeleton 141_4 may be a light-emitting skeleton, and thelight-emitting skeleton is preferably a skeleton capable of emittingphosphorescence (hereinafter also referred to as a phosphorescentskeleton). A structure in which a phosphorescent skeleton is used as theskeleton 141_4 will be described below. Note that the skeleton 141_4 maybe rephrased as the phosphorescent skeleton.

The skeleton 141_4 has a function similar to that of the guest material142. Thus, this structure example can be described by rephrasing theguest material 142 shown in Structure example 1 as the skeleton 141_4.Thus, Structure example 1 of this embodiment may be referred to for thedescription of functions similar to those in Structure example 1 of thisembodiment.

That is, the high molecular material 141 includes the skeleton having ahole-transport property included in the skeleton 141_1 and the skeletonhaving an electron-transport property included in the skeleton 1412, andtwo high molecular chains form an excited complex. Then, the excitationenergy is transferred from the excited complex to the skeleton 141_4,whereby light is emitted from the skeleton 141_4.

<Material that can be Used in Light-Emitting Layers>

Next, materials that can be used in the light-emitting layer 140 will bedescribed below.

The high molecular material 141 in the light-emitting layer 140 is notparticularly limited as long as two high molecular chains of the highmolecular material 141 have a function of forming an excited complex;however, the high molecular material 141 preferably includes aπ-electron deficient heteroaromatic skeleton and at least one of aπ-electron rich heteroaromatic skeleton and an aromatic amine skeleton.As the high molecular material 141, any of the materials described inEmbodiment 1 can be used.

As the guest material 142 (phosphorescent compound), an iridium-,rhodium-, or platinum-based organometallic complex or metal complex canbe used; in particular, an organoiridium complex such as aniridium-based ortho-metalated complex is preferable. As anortho-metalated ligand, a 4H-triazole ligand, a 1H-triazole ligand, animidazole ligand, a pyridine ligand, a pyrimidine ligand, a pyrazineligand, an isoquinoline ligand, and the like can be given. As the metalcomplex, a platinum complex having a porphyrin ligand and the like canbe given.

Examples of the substance that has an emission peak in the blue or greenwavelength range include organometallic iridium complexes having a4H-triazole skeleton, such as tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III)(abbreviation: Ir(mpptz-dmp)₃),tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III)(abbreviation: Ir(Mptz)₃),tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III)(abbreviation: Ir(iPrptz-3b)₃), andtris[3-(5-biphenyl)-5-isopropyl-4-phenyl-4H-1,2,4-triazolato]iridium(III)(abbreviation: Ir(iPr5btz)₃); organometallic iridium complexes having a1H-triazole skeleton, such astris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: Ir(Mptzl-mp)₃) andtris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III)(abbreviation: Ir(Prptzl-Me)₃); organometallic iridium complexes havingan imidazole skeleton, such asfac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III)(abbreviation: Ir(iPrpmi)₃) andtris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III)(abbreviation: Ir(dmpimpt-Me)₃); and organometallic iridium complexes inwhich a phenylpyridine derivative having an electron-withdrawing groupis a ligand, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III) picolinate(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate(abbreviation: Ir(CF3ppy)₂(pic)), andbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIr(acac)). Among the materials givenabove, the organometallic iridium complexes having a 4H-triazoleskeleton have high reliability and high light emission efficiency andare thus especially preferable.

Examples of the substance that has an emission peak in the green oryellow wavelength range include organometallic iridium complexes havinga pyrimidine skeleton, such astris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation:Ir(mppm)₃), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III)(abbreviation: Ir(tBuppm)₃),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(mppm)₂(acac)),(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(tBuppm)₂(acac)),(acetylacetonato)bis[4-(2-norbornyl)-6-phenylpyrimidinato]iridium(III)(abbreviation: Ir(nbppm)₂(acac)),(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: Ir(mpmppm)₂(acac)), (acetylacetonato)bis{4,6-dimethyl-2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}iridium(III)(abbreviation: Ir(dmppm-dmp)₂(acac)),(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: Ir(dppm)₂(acac)); organometallic iridium complexes havinga pyrazine skeleton, such as(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-Me)₂(acac)) and(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-iPr)₂(acac)); organometallic iridium complexeshaving a pyridine skeleton, such astris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(ppy)₂(acac)), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)₂(acac)),tris(benzo[h]quinolinato)iridium(III) (abbreviation: Ir(bzq)₃),tris(2-phenylquinolinato-N,C^(2′))iridium(III) (abbreviation: Ir(pq)₃),and bis(2-phenylquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(pq)₂(acac)); organometallic iridium complexes such asbis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(dpo)₂(acac)),bis{2-[4′-(perfluorophenyl)phenyl]pyridinato-N,C^(2′)}iridium(III)acetylacetonate(abbreviation: Ir(p-PF-ph)₂(acac)), andbis(2-phenylbenzothiazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(bt)₂(acac)); and a rare earth metal complex such astris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation:Tb(acac)₃(Phen)). Among the materials given above, the organometalliciridium complexes having a pyrimidine skeleton have distinctively highreliability and light emission efficiency and are thus particularlypreferable.

Examples of the substance that has an emission peak in the yellow or redwavelength range include organometallic iridium complexes having apyrimidine skeleton, such as(diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III)(abbreviation: Ir(5mdppm)₂(dibm)),bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: Ir(5mdppm)₂(dpm)), andbis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: Ir(dlnpm)₂(dpm)); organometallic iridium complexes havinga pyrazine skeleton, such as(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)₂(dpm)), and(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)); organometallic iridium complexes havinga pyridine skeleton, such astris(1-phenylisoquinolinato-N,C^(2′))iridium(III) (abbreviation:Ir(piq)₃) andbis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(piq)₂(acac)); a platinum complex such as2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II)(abbreviation: PtOEP); and rare earth metal complexes such astris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: Eu(DBM)₃(Phen)) andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: Eu(TTA)₃(Phen)). Among the materials given above, theorganometallic iridium complexes having a pyrimidine skeleton havedistinctively high reliability and light emission efficiency and arethus particularly preferable. Further, the organometallic iridiumcomplexes having a pyrazine skeleton can provide red light emission withfavorable chromaticity.

As the light-emitting material included in the light-emitting layer 140,any material can be used as long as the material can convert the tripletexcitation energy into light emission. As an example of the materialthat can convert the triplet excitation energy into light emission, athermally activated delayed fluorescent (TADF) material can be given inaddition to a phosphorescent compound. Therefore, it is acceptable thatthe “phosphorescent compound” in the description is replaced with the“thermally activated delayed fluorescence material”. Note that thethermally activated delayed fluorescence material is a material having asmall difference between the triplet excitation energy level and thesinglet excitation energy level and a function of converting tripletexcitation energy into singlet excitation energy by reverse intersystemcrossing. Thus, the TADF material can up-convert a triplet excited stateinto a singlet excited state (i.e., reverse intersystem crossing ispossible) using a little thermal energy and efficiently exhibit lightemission (fluorescence) from the singlet excited state. The TADF isefficiently obtained under the condition where the difference in energybetween the triplet excitation energy level and the singlet excitationenergy level is preferably larger than 0 eV and smaller than or equal to0.2 eV, further preferably larger than 0 eV and smaller than or equal to0.1 eV.

In the case where the material exhibiting thermally activated delayedfluorescence is formed of one kind of material, any of the thermallyactivated delayed fluorescent materials described in Embodiment 1 can bespecifically used.

The guest material 142 may be a high molecular compound, and forexample, a high molecular compound including an iridium-, rhodium-, orplatinum-based organometallic complex or metal complex as a structuralunit is preferable.

In the light-emitting layer 140, the skeleton 1414 is not particularlylimited; however, a light-emitting skeleton which is included in theguest material 142 is preferably included in the skeleton 141_4. Thatis, a structure where one or two hydrogen atoms are removed from theiridium-, rhodium-, or platinum-based organometallic complex or metalcomplex is preferably used as the structural unit.

The light-emitting layer 140 can have a structure in which two or morelayers are stacked. For example, in the case where the light-emittinglayer 140 is formed by stacking a first light-emitting layer and asecond light-emitting layer in this order from the hole-transport layerside, the first light-emitting layer is formed using a substance havinga hole-transport property as the high molecular material and the secondlight-emitting layer is formed using a substance having anelectron-transport property as the high molecular material.

The light-emitting layer 140 may include another material in addition tothe high molecular material 141 and the guest material 142.Specifically, any of the materials described in Embodiment 1 can beused.

Note that the light-emitting layer 140 can be formed by an evaporationmethod (including a vacuum evaporation method), an inkjet method, acoating method, a nozzle-printing method, gravure printing, or the like.Besides the above-mentioned materials, an inorganic compound such as aquantum dot or a high molecular compound (e.g., an oligomer, adendrimer, and a polymer) may be used.

The structure described in this embodiment can be used in appropriatecombination with any of the structures described in the otherembodiments.

Embodiment 3

In this embodiment, examples of light-emitting elements havingstructures different from those described in Embodiments 1 and 2 aredescribed below with reference to FIGS. 5A and 5B, FIGS. 6A and 6B,FIGS. 7A to 7C, and FIGS. 8A and 8B.

Structure Example 1 of Light-Emitting Element

FIGS. 5A and 5B are cross-sectional views each illustrating alight-emitting element of one embodiment of the present invention. InFIGS. 5A and 5B, a portion having a function similar to that in FIG. 1Ais represented by the same hatch pattern as in FIG. 1A and notespecially denoted by a reference numeral in some cases. In addition,common reference numerals are used for portions having similarfunctions, and a detailed description of the portions is omitted in somecases.

Light-emitting elements 260 a and 260 b in FIGS. 5A and 5B may have abottom-emission structure in which light is extracted through thesubstrate 200 or may have a top-emission structure in which lightemitted from the light-emitting element is extracted in the directionopposite to the substrate 200. However, one embodiment of the presentinvention is not limited to this structure, and a light-emitting elementhaving a dual-emission structure in which light emitted from thelight-emitting element is extracted in both top and bottom directions ofthe substrate 200 may be used.

In the case where the light-emitting elements 260 a and 260 b each havea bottom emission structure, the electrode 101 preferably has a functionof transmitting light and the electrode 102 preferably has a function ofreflecting light. Alternatively, in the case where the light-emittingelements 260 a and 260 b each have a top emission structure, theelectrode 101 preferably has a function of reflecting light and theelectrode 102 preferably has a function of transmitting light.

The light-emitting elements 260 a and 260 b each include the electrode101 and the electrode 102 over the substrate 200. Between the electrodes101 and 102, a light-emitting layer 123B, a light-emitting layer 123G,and a light-emitting layer 123R are provided. The hole-injection layer111, the hole-transport layer 112, the electron-transport layer 113, andthe electron-injection layer 114 are also provided.

The light-emitting element 260 b includes, as part of the electrode 101,a conductive layer 101 a, a conductive layer 101 b over the conductivelayer 101 a, and a conductive layer 101 c under the conductive layer 101a. In other words, the light-emitting element 260 b includes theelectrode 101 having a structure in which the conductive layer 101 a issandwiched between the conductive layer 101 b and the conductive layer101 c.

In the light-emitting element 260 b, the conductive layer 101 b and theconductive layer 101 c may be formed with different materials or thesame material. The electrode 101 preferably has a structure in which theconductive layer 101 a is sandwiched by the layers formed of the sameconductive material, in which case patterning by etching can beperformed easily.

In the light-emitting element 260 b, the electrode 101 may include oneof the conductive layer 101 b and the conductive layer 101 c.

For each of the conductive layers 101 a, 101 b, and 101 c, which areincluded in the electrode 101, the structure and materials of theelectrode 101 or 102 described in Embodiment 1 can be used.

In FIGS. 5A and 5B, a partition wall 145 is provided between a region221B, a region 221G, and a region 221R, which are sandwiched between theelectrode 101 and the electrode 102. The partition wall 145 has aninsulating property. The partition wall 145 covers end portions of theelectrode 101 and has openings overlapping with the electrode. With thepartition wall 145, the electrode 101 provided over the substrate 200 inthe regions can be divided into island shapes.

Note that the light-emitting layer 123B and the light-emitting layer123G may overlap with each other in a region where they overlap with thepartition wall 145. The light-emitting layer 123G and the light-emittinglayer 123R may overlap with each other in a region where they overlapwith the partition wall 145. The light-emitting layer 123R and thelight-emitting layer 123B may overlap with each other in a region wherethey overlap with the partition wall 145.

The partition wall 145 has an insulating property and is formed using aninorganic or organic material. Examples of the inorganic materialinclude silicon oxide, silicon oxynitride, silicon nitride oxide,silicon nitride, aluminum oxide, and aluminum nitride. Examples of theorganic material include photosensitive resin materials such as anacrylic resin and a polyimide resin.

Note that a silicon oxynitride film refers to a film in which theproportion of oxygen is higher than that of nitrogen. The siliconoxynitride film preferably contains oxygen, nitrogen, silicon, andhydrogen in the ranges of 55 atomic % to 65 atomic %, 1 atomic % to 20atomic %, 25 atomic % to 35 atomic %, and 0.1 atomic % to 10 atomic %,respectively. A silicon nitride oxide film refers to a film in which theproportion of nitrogen is higher than that of oxygen. The siliconnitride oxide film preferably contains nitrogen, oxygen, silicon, andhydrogen in the ranges of 55 atomic % to 65 atomic %, 1 atomic % to 20atomic %, 25 atomic % to 35 atomic %, and 0.1 atomic % to 10 atomic %,respectively.

The light-emitting layers 123R, 123G, and 123B preferably containlight-emitting materials having functions of emitting light of differentcolors. For example, when the light-emitting layer 123R contains alight-emitting material having a function of emitting red, the region221R emits red light. When the light-emitting layer 123G contains alight-emitting material having a function of emitting green, the region221G emits green light. When the light-emitting layer 123B contains alight-emitting material having a function of emitting blue, the region221B emits blue light. The light-emitting element 260 a or 260 b havingsuch a structure is used in a pixel of a display device, whereby afull-color display device can be fabricated. The thicknesses of thelight-emitting layers may be the same or different.

Any one or more of the light-emitting layers 123B, 123G, and 123Rpreferably include at least one of the light-emitting layer 130described in Embodiment 1 and the light-emitting layer 140 described inEmbodiment 2, in which case a light-emitting element with high lightemission efficiency can be fabricated.

One or more of the light-emitting layers 123B, 123G, and 123R mayinclude two or more stacked layers.

When at least one light-emitting layer includes the light-emitting layerdescribed in Embodiment 1 or 2 as described above and the light-emittingelement 260 a or 260 b including the light-emitting layer is used inpixels in a display device, a display device with high light emissionefficiency can be fabricated. The display device including thelight-emitting element 260 a or 260 b can thus have reduced powerconsumption.

By providing an optical element (e.g., a color filter, a polarizingplate, and an anti-reflection film) on the light extraction side of theelectrode through which light is extracted, the color purity of each ofthe light-emitting elements 260 a and 260 b can be improved. Therefore,the color purity of a display device including the light-emittingelement 260 a or 260 b can be improved. Alternatively, the reflection ofexternal light by each of the light-emitting elements 260 a and 260 bcan be reduced. Therefore, the contrast ratio of a display deviceincluding the light-emitting element 260 a or 260 b can be improved.

For the other components of the light-emitting elements 260 a and 260 b,the components of the light-emitting elements in Embodiments 1 and 2 maybe referred to.

Structure Example 2 of Light-Emitting Element

Next, structure examples of the light-emitting elements different fromthose in FIGS. 5A and 5B will be described below with reference to FIGS.6A and 6B.

FIGS. 6A and 6B are cross-sectional views of a light-emitting element ofone embodiment of the present invention. In FIGS. 6A and 6B, a portionhaving a function similar to that in FIGS. 5A and 5B is represented bythe same hatch pattern as in FIGS. 5A and 5B and not especially denotedby a reference numeral in some cases. In addition, common referencenumerals are used for portions having similar functions, and a detaileddescription of such portions is not repeated in some cases.

FIGS. 6A and 6B illustrate structure examples of a light-emittingelement including the light-emitting layer between a pair of electrodes.A light-emitting element 262 a illustrated in FIG. 6A has a top-emissionstructure in which light is extracted in a direction opposite to thesubstrate 200, and a light-emitting element 262 b illustrated in FIG. 6Bhas a bottom-emission structure in which light is extracted to thesubstrate 200 side. However, one embodiment of the present invention isnot limited to these structures and may have a dual-emission structurein which light emitted from the light-emitting element is extracted inboth top and bottom directions with respect to the substrate 200 overwhich the light-emitting element is formed.

The light-emitting elements 262 a and 262 b each include the electrode101, the electrode 102, an electrode 103, and an electrode 104 over thesubstrate 200. At least a light-emitting layer 170 is provided betweenthe electrode 101 and the electrode 102, between the electrode 102 andthe electrode 103, and between the electrode 102 and the electrode 104.The hole-injection layer 111, the hole-transport layer 112, theelectron-transport layer 113, and the electron-injection layer 114 arefurther provided.

The electrode 101 includes a conductive layer 101 a and a conductivelayer 101 b over and in contact with the conductive layer 101 a. Theelectrode 103 includes a conductive layer 103 a and a conductive layer103 b over and in contact with the conductive layer 103 a. The electrode104 includes a conductive layer 104 a and a conductive layer 104 b overand in contact with the conductive layer 104 a.

The light-emitting element 262 a illustrated in FIG. 6A and thelight-emitting element 262 b illustrated in FIG. 6B each include apartition wall 145 between a region 222B sandwiched between theelectrode 101 and the electrode 102, a region 222G sandwiched betweenthe electrode 102 and the electrode 103, and a region 222R sandwichedbetween the electrode 102 and the electrode 104. The partition wall 145has an insulating property. The partition wall 145 covers end portionsof the electrodes 101, 103, and 104 and has openings overlapping withthe electrodes. With the partition wall 145, the electrodes providedover the substrate 200 in the regions can be separated into islandshapes.

The light-emitting elements 262 a and 262 b each include a substrate 220provided with an optical element 224B, an optical element 224G, and anoptical element 224R in the direction in which light emitted from theregion 222B, light emitted from the region 222G, and light emitted fromthe region 222R are extracted. The light emitted from each region isemitted outside the light-emitting element through each optical element.In other words, the light from the region 222B, the light from theregion 222G, and the light from the region 222R are emitted through theoptical element 224B, the optical element 224G, and the optical element224R, respectively.

The optical elements 224B, 224G, and 224R each have a function ofselectively transmitting light of a particular color out of incidentlight. For example, the light emitted from the region 222B through theoptical element 224B is blue light, the light emitted from the region222G through the optical element 224G is green light, and the lightemitted from the region 222R through the optical element 224R is redlight.

For example, a coloring layer (also referred to as color filter), a bandpass filter, a multilayer filter, or the like can be used for theoptical elements 224R, 224G, and 224B. Alternatively, color conversionelements can be used as the optical elements. A color conversion elementis an optical element that converts incident light into light having alonger wavelength than the incident light. As the color conversionelements, quantum-dot elements can be favorably used. The usage of thequantum-dot type can increase color reproducibility of the displaydevice.

One or more of optical elements may further be stacked over each of theoptical elements 224R, 224G, and 224B. As another optical element, acircularly polarizing plate, an anti-reflective film, or the like can beprovided, for example. A circularly polarizing plate provided on theside where light emitted from the light-emitting element of the displaydevice is extracted can prevent a phenomenon in which light enteringfrom the outside of the display device is reflected inside the displaydevice and returned to the outside. An anti-reflective film can weakenexternal light reflected by a surface of the display device. This leadsto clear observation of light emitted from the display device.

Note that in FIGS. 6A and 6B, blue light (B), green light (G), and redlight (R) emitted from the regions through the optical elements areschematically illustrated by arrows of dashed lines.

Alight-blocking layer 223 is provided between the optical elements. Thelight-blocking layer 223 has a function of blocking light emitted fromthe adjacent regions. Note that a structure without the light-blockinglayer 223 may also be employed.

The light-blocking layer 223 has a function of reducing the reflectionof external light. The light-blocking layer 223 has a function ofpreventing mixture of light emitted from an adjacent light-emittingelement. As the light-blocking layer 223, a metal, a resin containingblack pigment, carbon black, a metal oxide, a composite oxide containinga solid solution of a plurality of metal oxides, or the like can beused.

Note that the optical element 224B and the optical element 224G mayoverlap with each other in a region where they overlap with thelight-blocking layer 223. In addition, the optical element 224G and theoptical element 224R may overlap with each other in a region where theyoverlap with the light-blocking layer 223. In addition, the opticalelement 224R and the optical element 224B may overlap with each other ina region where they overlap with the light-blocking layer 223.

For the substrate 200 and the substrate 220 provided with the opticalelements, the substrate in Embodiment 1 may be referred to.

Furthermore, the light-emitting elements 262 a and 262 b have amicrocavity structure.

<<Microcavity Structure>>

Light emitted from the light-emitting layer 170 resonates between a pairof electrodes (e.g., the electrode 101 and the electrode 102). Thelight-emitting layer 170 is formed at such a position as to intensifythe light of a desired wavelength among light to be emitted. Forexample, by adjusting the optical length from a reflective region of theelectrode 101 to the light-emitting region of the light-emitting layer170 and the optical length from a reflective region of the electrode 102to the light-emitting region of the light-emitting layer 170, the lightof a desired wavelength among light emitted from the light-emittinglayer 170 can be intensified.

In each of the light-emitting elements 262 a and 262 b, by adjusting thethicknesses of the conductive layers (the conductive layer 101 b, theconductive layer 103 b, and the conductive layer 104 b) in each region,the light of a desired wavelength among light emitted from thelight-emitting layer 170 can be increased. Note that the thickness of atleast one of the hole-injection layer 111 and the hole-transport layer112 may differ between the regions to increase the light emitted fromthe light-emitting layer 170.

For example, in the case where the refractive index of the conductivematerial having a function of reflecting light in the electrodes 101 to104 is lower than the refractive index of the light-emitting layer 170,the thickness of the conductive layer 101 b of the electrode 101 isadjusted so that the optical length between the electrode 101 and theelectrode 102 is m_(B)λ_(B)/2 (m_(B) is a natural number and λ_(B) isthe wavelength of light intensified in the region 222B). Similarly, thethickness of the conductive layer 103 b of the electrode 103 is adjustedso that the optical length between the electrode 103 and the electrode102 is m_(G)λ_(G)/2 (m_(G) is a natural number and λ_(G) is thewavelength of light intensified in the region 222G). Furthermore, thethickness of the conductive layer 104 b of the electrode 104 is adjustedso that the optical length between the electrode 104 and the electrode102 is m_(R)λ_(R)/2 (m_(R) is a natural number and λ_(R) is thewavelength of light intensified in the region 222R).

In the case where it is difficult to precisely determine the reflectiveregions of the electrodes 101 to 104, the optical length forintensifying light emitted from the light-emitting layer 170 may bederived on the assumption that certain regions of the electrodes 101 to104 are the reflective regions. In the case where it is difficult toprecisely determine the light-emitting region of the light-emittinglayer 170, the optical length for intensifying light emitted from thelight-emitting layer 170 may be derived on the assumption that certainregion of the light-emitting layer 170 is the light-emitting region.

In the above manner, with the microcavity structure, in which theoptical length between the pair of electrodes in the respective regionsis adjusted, scattering and absorption of light in the vicinity of theelectrodes can be suppressed, resulting in high light extractionefficiency. In the above structure, the conductive layers 101 b, 103 b,and 104 b preferably have a function of transmitting light. Thematerials of the conductive layers 101 b, 103 b, and 104 b may be thesame or different. The conductive layers 101 b, 103 b, and 104 b arepreferably formed using the same materials, in which case patterning byetching can be performed easily. Each of the conductive layers 101 b,103 b, and 104 b may have a stacked structure of two or more layers.

Since the light-emitting element 262 a illustrated in FIG. 6A has atop-emission structure, it is preferable that the conductive layer 101a, the conductive layer 103 a, and the conductive layer 104 a have afunction of reflecting light. In addition, it is preferable that theelectrode 102 have functions of transmitting light and reflecting light.

Since the light-emitting element 262 b illustrated in FIG. 6B has abottom-emission structure, it is preferable that the conductive layer101 a, the conductive layer 103 a, and the conductive layer 104 a havefunctions of transmitting light and reflecting light. In addition, it ispreferable that the electrode 102 have a function of reflecting light.

In each of the light-emitting elements 262 a and 262 b, the conductivelayers 101 a, 103 a, and 104 a may be formed of different materials orthe same material. When the conductive layers 101 a, 103 a, and 104 aare formed of the same material, manufacturing cost of thelight-emitting elements 262 a and 262 b can be reduced. Note that eachof the conductive layers 101 a, 103 a, and 104 a may have a stackedstructure including two or more layers.

The light-emitting layer 170 in the light-emitting elements 262 a and262 b preferably has the structure described in Embodiment 1 or 2, inwhich case light-emitting elements with high light emission efficiencycan be fabricated.

The light-emitting layer 170 may have a stacked structure of two layers.The two light-emitting layers including two kinds of light-emittingmaterials (a first compound and a second compound) for emittingdifferent colors of light enable light emission of a plurality ofcolors. It is particularly preferable to select the light-emittingmaterials of the light-emitting layers so that white light can beobtained by combining light emissions from the light-emitting layer 170.

The light-emitting layer 170 may have a stacked structure of three ormore layers, in which a layer not including a light-emitting materialmay be included.

In the above-described manner, the light-emitting element 262 a or 262 bincluding at least one of the light-emitting layers which have thestructures described in Embodiments 1 and 2 is used in pixels in adisplay device, whereby a display device with high light emissionefficiency can be fabricated. Accordingly, the display device includingthe light-emitting element 262 a or 262 b can have low powerconsumption.

For the other components of the light-emitting elements 262 a and 262 b,the components of the light-emitting elements 260 a and 260 b and thelight-emitting elements in Embodiments 1 and 2 may be referred to.

<Fabrication Method of Light-Emitting Element>

Next, a method for fabricating a light-emitting element of oneembodiment of the present invention is described below with reference toFIGS. 7A to 7C and FIGS. 8A and 8B. Here, a method for fabricating thelight-emitting element 262 a illustrated in FIG. 6A is described.

FIGS. 7A to 7C and FIGS. 8A and 8B are cross-sectional viewsillustrating a method for fabricating the light-emitting element of oneembodiment of the present invention.

The method for manufacturing the light-emitting element 262 a describedbelow includes first to sixth steps.

<<First Step>>

In the first step, the electrodes (specifically the conductive layer 101a of the electrode 101, the conductive layer 103 a of the electrode 103,and the conductive layer 104 a of the electrode 104) of thelight-emitting elements are formed over the substrate 200 (see FIG. 7A).

In this embodiment, a conductive layer having a function of reflectinglight is formed over the substrate 200 and processed into a desiredshape; whereby the conductive layers 101 a, 103 a, and 104 a are formed.As the conductive layer having a function of reflecting light, an alloyfilm of silver, palladium, and copper (also referred to as an Ag—Pd—Cufilm or APC) is used. The conductive layers 101 a, 103 a, and 104 a arepreferably formed through a step of processing the same conductivelayer, because the manufacturing cost can be reduced.

Note that a plurality of transistors may be formed over the substrate200 before the first step. The plurality of transistors may beelectrically connected to the conductive layers 101 a, 103 a, and 104 a.

<<Second Step>>

In the second step, the conductive layer 101 b having a function oftransmitting light is formed over the conductive layer 101 a of theelectrode 101, the conductive layer 103 b having a function oftransmitting light is formed over the conductive layer 103 a of theelectrode 103, and the conductive layer 104 b having a function oftransmitting light is formed over the conductive layer 104 a of theelectrode 104 (see FIG. 7B).

In this embodiment, the conductive layers 101 b, 103 b, and 104 b eachhaving a function of transmitting light are formed over the conductivelayers 101 a, 103 a, and 104 a each having a function of reflectinglight, respectively, whereby the electrode 101, the electrode 103, andthe electrode 104 are formed. As the conductive layers 101 b, 103 b, and104 b, ITSO films are used.

The conductive layers 101 b, 103 b, and 104 b having a function oftransmitting light may be formed through a plurality of steps. When theconductive layers 101 b, 103 b, and 104 b having a function oftransmitting light are formed through a plurality of steps, they can beformed to have thicknesses which enable microcavity structuresappropriate in the respective regions.

<<Third Step>>

In the third step, the partition wall 145 that covers end portions ofthe electrodes of the light-emitting element is formed (see FIG. 7C).

The partition wall 145 includes an opening overlapping with theelectrode. The conductive film exposed by the opening functions as theanode of the light-emitting element. As the partition wall 145, apolyimide-based resin is used in this embodiment.

In the first to third steps, since there is no possibility of damagingthe EL layer (a layer containing an organic compound), a variety of filmformation methods and fine processing technologies can be employed. Inthis embodiment, a reflective conductive layer is formed by a sputteringmethod, a pattern is formed over the conductive layer by a lithographymethod, and then the conductive layer is processed into an island shapeby a dry etching method or a wet etching method to form the conductivelayer 101 a of the electrode 101, the conductive layer 103 a of theelectrode 103, and the conductive layer 104 a of the electrode 104.Then, a transparent conductive film is formed by a sputtering method, apattern is formed over the transparent conductive film by a lithographymethod, and then the transparent conductive film is processed intoisland shapes by a wet etching method to form the electrodes 101, 103,and 104.

<<Fourth Step>>

In the fourth step, the hole-injection layer 111, the hole-transportlayer 112, the light-emitting layer 170, the electron-transport layer113, the electron-injection layer 114, and the electrode 102 are formed(see FIG. 8A).

The hole-injection layer 111 can be formed by spin-coatingpoly(ethylenedioxythiophene)/poly(styrenesulfonic acid), for example.The hole-transport layer 112 which can be formed using a hole-transportmaterial can be formed by spin-coating polyvinylcarbazole, for example.After the formation of the hole-injection layer 111 and thehole-transport layer 112, heat treatment may be performed under an airatmosphere or an inert gas atmosphere such as nitrogen.

The light-emitting layer 170 can be formed using a high molecularmaterial that emits light of at least one of violet, blue, blue green,green, yellow green, yellow, orange, and red. As the high molecularmaterial, a fluorescent or phosphorescent organic compound can be used.The light-emitting layer 170 can be formed in such a manner that asolvent in which the high molecular material is dissolved is coatedusing a spin-coating method or the like. After the formation of thelight-emitting layer 170, heat treatment may be performed under an airatmosphere or an inert gas atmosphere such as nitrogen. The fluorescentor phosphorescent organic compound may be used as a guest material, andthe guest material may be dispersed into a high molecular materialhaving higher excitation energy than the guest material. Thelight-emitting organic compound may be deposited alone or thelight-emitting organic compound mixed with another material may bedeposited. The light-emitting layer 170 may have a two-layer structure.In that case, the two light-emitting layers preferably containlight-emitting substances that emit light of different colors.

The electron-transport layer 113 can be formed using a substance havinga high electron-transport property. The electron-injection layer 114 canbe formed using a substance having a high electron-injection property.Note that the electron-transport layer 113 and the electron-injectionlayer 114 can be formed by an evaporation method.

The electrode 102 can be formed by stacking a reflective conductive filmand a light-transmitting conductive film. The electrode 102 may have asingle-layer structure or a stacked-layer structure.

Through the above-described steps, the light-emitting element includingthe region 222B, the region 222G, and the region 222R over the electrode101, the electrode 103, and the electrode 104, respectively, are formedover the substrate 200.

<<Fifth Step>>

In the fifth step, the light-blocking layer 223, the optical element224B, the optical element 224G, and the optical element 224R are formedover the substrate 220 (see FIG. 8B).

As the light-blocking layer 223, a resin film containing black pigmentis formed in a desired region. Then, the optical element 224B, theoptical element 224G, and the optical element 224R are formed over thesubstrate 220 and the light-blocking layer 223. As the optical element224B, a resin film containing blue pigment is formed in a desiredregion. As the optical element 224G, a resin film containing greenpigment is formed in a desired region. As the optical element 224R, aresin film containing red pigment is formed in a desired region.

<<Sixth Step>>

In the sixth step, the light-emitting element formed over the substrate200 is attached to the light-blocking layer 223, the optical element224B, the optical element 224G, and the optical element 224R formed overthe substrate 220, and sealed with a sealant (not illustrated).

Through the above-described steps, the light-emitting element 262 aillustrated in FIG. 6A can be formed.

Note that the structures described in this embodiment can be used inappropriate combination with any of the structures described in theother embodiments.

Embodiment 4

In this embodiment, a display device of one embodiment of the presentinvention will be described below with reference to FIGS. 9A and 9B,FIGS. 10A and 10B, FIG. 11, FIGS. 12A and 12B, FIGS. 13A and 13B, FIG.14, FIGS. 15A and 15B, FIG. 16, FIGS. 17A and 17B, FIGS. 18A to 18D, andFIG. 19.

Structure Example 1 of Display Device

FIG. 9A is a top view illustrating a display device 600 and FIG. 9B is across-sectional view taken along the dashed-dotted line A-B and thedashed-dotted line C-D in FIG. 9A. The display device 600 includesdriver circuit portions (a signal line driver circuit portion 601 and ascan line driver circuit portion 603) and a pixel portion 602. Note thatthe signal line driver circuit portion 601, the scan line driver circuitportion 603, and the pixel portion 602 have a function of controllinglight emission of a light-emitting element.

The display device 600 also includes an element substrate 610, a sealingsubstrate 604, a sealant 605, a region 607 surrounded by the sealant605, a lead wiring 608, and an FPC 609.

Note that the lead wiring 608 is a wiring for transmitting signals to beinput to the signal line driver circuit portion 601 and the scan linedriver circuit portion 603 and for receiving a video signal, a clocksignal, a start signal, a reset signal, and the like from the FPC 609serving as an external input terminal. Although only the FPC 609 isillustrated here, the FPC 609 may be provided with a printed wiringboard (PWB).

As the signal line driver circuit portion 601, a CMOS circuit in whichan n-channel transistor 623 and a p-channel transistor 624 are combinedis formed. As the signal line driver circuit portion 601 or the scanline driver circuit portion 603, various types of circuits such as aCMOS circuit, a PMOS circuit, or an NMOS circuit can be used. Although adriver in which a driver circuit portion is formed and a pixel areformed over the same surface of a substrate in the display device ofthis embodiment, the driver circuit portion is not necessarily formedover the substrate and can be formed outside the substrate.

The pixel portion 602 includes a switching transistor 611, a currentcontrol transistor 612, and a lower electrode 613 electrically connectedto a drain of the current control transistor 612. Note that a partitionwall 614 is formed to cover end portions of the lower electrode 613. Asthe partition wall 614, for example, a positive type photosensitiveacrylic resin film can be used.

In order to obtain favorable coverage by a film which is formed over thepartition wall 614, the partition wall 614 is formed to have a curvedsurface with curvature at its upper or lower end portion. For example,in the case of using a positive photosensitive acrylic as a material ofthe partition wall 614, it is preferable that only the upper end portionof the partition wall 614 have a curved surface with curvature (theradius of the curvature being 0.2 μm to 3 μm). As the partition wall614, either a negative photosensitive resin or a positive photosensitiveresin can be used.

Note that there is no particular limitation on a structure of each ofthe transistors (the transistors 611, 612, 623, and 624). For example, astaggered transistor can be used. In addition, there is no particularlimitation on the polarity of these transistors. For these transistors,n-channel and p-channel transistors may be used, or either n-channeltransistors or p-channel transistors may be used, for example.Furthermore, there is no particular limitation on the crystallinity of asemiconductor film used for these transistors. For example, an amorphoussemiconductor film or a crystalline semiconductor film may be used.Examples of a semiconductor material include Group 14 semiconductors(e.g., a semiconductor including silicon), compound semiconductors(including oxide semiconductors), organic semiconductors, and the like.For example, it is preferable to use an oxide semiconductor that has anenergy gap of 2 eV or more, preferably 2.5 eV or more and furtherpreferably 3 eV or more, for the transistors, so that the off-statecurrent of the transistors can be reduced. Examples of the oxidesemiconductor include an In—Ga oxide and an In-M-Zn oxide (M is Al, Ga,Y, zirconium (Zr), La, cerium (Ce), Sn, hafnium (Hf), or Nd).

An EL layer 616 and an upper electrode 617 are formed over the lowerelectrode 613. Here, the lower electrode 613 functions as an anode andthe upper electrode 617 functions as a cathode.

In addition, the EL layer 616 is formed by various methods such as anevaporation method with an evaporation mask, an ink-jet method, or aspin coating method. As another material included in the EL layer 616, alow molecular compound or a high molecular compound may be used.

Note that a light-emitting element 618 is formed with the lowerelectrode 613, the EL layer 616, and the upper electrode 617. Thelight-emitting element 618 preferably has any of the structuresdescribed in Embodiments 1 to 3. In the case where the pixel portionincludes a plurality of light-emitting elements, the pixel portion mayinclude both any of the light-emitting elements described in Embodiments1 to 3 and a light-emitting element having a different structure.

When the sealing substrate 604 and the element substrate 610 areattached to each other with the sealant 605, the light-emitting element618 is provided in the region 607 surrounded by the element substrate610, the sealing substrate 604, and the sealant 605. The region 607 isfilled with a filler. In some cases, the region 607 is filled with aninert gas (nitrogen, argon, or the like) or filled with an ultravioletcurable resin or a thermosetting resin which can be used for the sealant605. For example, a polyvinyl chloride (PVC)-based resin, anacrylic-based resin, a polyimide-based resin, an epoxy-based resin, asilicone-based resin, a polyvinyl butyral (PVB)-based resin, or anethylene vinyl acetate (EVA)-based resin can be used. It is preferablethat the sealing substrate be provided with a recessed portion and thedesiccant be provided in the recessed portion, in which casedeterioration due to influence of moisture can be inhibited.

An optical element 621 is provided below the sealing substrate 604 tooverlap with the light-emitting element 618. A light-blocking layer 622is provided below the sealing substrate 604. The structures of theoptical element 621 and the light-blocking layer 622 can be the same asthose of the optical element and the light-blocking layer in Embodiment3, respectively.

An epoxy-based resin or glass frit is preferably used for the sealant605. It is preferable that such a material do not transmit moisture oroxygen as much as possible. As the sealing substrate 604, a glasssubstrate, a quartz substrate, or a plastic substrate formed of fiberreinforced plastic (FRP), poly(vinyl fluoride) (PVF), polyester,acrylic, or the like can be used.

Here, a method for forming the EL layer 616 by a droplet dischargemethod is described with reference to FIGS. 18A to 18D. FIGS. 18A to 18Dare cross-sectional views illustrating the method for forming the ELlayer 616.

First, the element substrate 610 over which the lower electrode 613 andthe partition wall 614 are formed is illustrated in FIG. 18A. However,as in FIG. 9B, the lower electrode 613 and the partition wall 614 may beformed over an insulating film over a substrate.

Next, in a portion where the lower electrode 613 is exposed, which is anopening portion of the partition wall 614, a droplet 684 is dischargedfrom a droplet discharge apparatus 683 to form a layer 685 containing acomposition. The droplet 684 is a composition containing a solvent andis attached to the lower electrode 613 (see FIG. 18B).

Note that the method for discharging the droplet 684 may be performedunder reduced pressure.

Then, the solvent is removed from the layer 685 containing thecomposition, and the resulting layer is solidified to form the EL layer616 (see FIG. 18C).

The solvent may be removed by drying or heating.

Next, the upper electrode 617 is formed over the EL layer 616, and thelight-emitting element 618 is formed (see FIG. 18D).

When the EL layer 616 is formed by a droplet discharge method asdescribed above, the composition can be selectively discharged, andaccordingly, loss of materials can be reduced. Furthermore, alithography process or the like for shaping is not needed, and thus, theprocess can be simplified and cost reduction can be achieved.

The droplet discharge method described above is a general term for ameans including a nozzle equipped with a composition discharge openingor a means to discharge droplets such as a head having one or aplurality of nozzles.

Next, a droplet discharge apparatus used for the droplet dischargemethod is described with reference to FIG. 19. FIG. 19 is a conceptualdiagram illustrating a droplet discharge apparatus 1400.

The droplet discharge apparatus 1400 includes a droplet discharge means1403. In addition, the droplet discharge means 1403 is equipped with ahead 1405 and a head 1412.

The heads 1405 and 1412 are connected to a control means 1407, and thiscontrol means 1407 is controlled by a computer 1410; thus, apreprogrammed pattern can be drawn.

The drawing may be conducted at a timing, for example, based on a marker1411 formed over a substrate 1402. Alternatively, the reference pointmay be determined on the basis of an outer edge of the substrate 1402.Here, the marker 1411 is detected by an imaging means 1404 and convertedinto a digital signal by an image processing means 1409. Then, thedigital signal is recognized by the computer 1410, and then, a controlsignal is generated and transmitted to the control means 1407.

An image sensor or the like using a charge coupled device (CCD) or acomplementary metal oxide semiconductor (CMOS) can be used for theimaging means 1404. Note that information on a pattern to be formed overthe substrate 1402 is stored in a storage medium 1408, and the controlsignal is transmitted to the control means 1407 on the basis of theinformation, whereby the head 1405 and the head 1412 of the dropletdischarge means 1403 can be separately controlled. A material to bedischarged is supplied to the head 1405 and the head 1412 from amaterial source 1413 and a material source 1414, respectively, throughpipes.

Inside the head 1405, a space 1406 filled with a liquid material asindicated by a dotted line and a nozzle serving as a discharge openingare provided. Although not illustrated, an internal structure of thehead 1412 is similar to that of the head 1405. When the nozzle sizes ofthe heads 1405 and 1412 are different from each other, patterns ofdifferent materials can be drawn with different widths simultaneously.Alternatively, one head can discharge plural kinds of light-emittingmaterials or the like and draw a pattern. When a pattern is drawn in alarge area, the same material can be simultaneously discharged from aplurality of nozzles and the pattern can be drawn to improve throughput.When a large substrate is used, the heads 1405 and 1412 can freely scanthe substrate in directions indicated by arrows X, Y, and Z in FIG. 19,and a region in which a pattern is drawn can be freely set. Thus, aplurality of the same patterns can be drawn over one substrate.

In addition, the step of discharging the composition may be performedunder reduced pressure. The substrate may be heated when the compositionis discharged. After the composition is discharged, either or both stepsof drying and baking are performed. Both the drying and baking steps areheat treatment steps but different in purpose, temperature, and timeperiod. The steps of drying and baking are each performed under normalpressure or reduced pressure, by laser light irradiation, rapid thermalannealing, heating using a heating furnace, or the like. Note that thereis no particular limitation on the timing and the number of steps ofthis heat treatment. The temperature for performing each of the steps ofdrying and baking in a favorable manner depends on the materials of thesubstrate and the properties of the composition.

In the above-described manner, the display device including any of thelight-emitting elements and the optical elements which are described inEmbodiments 1 to 3 can be obtained.

Structure Example 2 of Display Device

Next, another example of the display device is described with referenceto FIGS. 10A and 10B and FIG. 11. Note that FIGS. 10A and 10B and FIG.11 are each a cross-sectional view of a display device of one embodimentof the present invention.

In FIG. 10A, a substrate 1001, a base insulating film 1002, a gateinsulating film 1003, gate electrodes 1006, 1007, and 1008, a firstinterlayer insulating film 1020, a second interlayer insulating film1021, a peripheral portion 1042, a pixel portion 1040, a driver circuitportion 1041, lower electrodes 1024R, 1024G, and 1024B of light-emittingelements, a partition wall 1025, an EL layer 1028, an upper electrode1026 of the light-emitting elements, a sealing layer 1029, a sealingsubstrate 1031, a sealant 1032, and the like are illustrated.

In FIG. 10A, examples of the optical elements, coloring layers (a redcoloring layer 1034R, a green coloring layer 1034G, and a blue coloringlayer 1034B) are provided on a transparent base material 1033. Further,a light-blocking layer 1035 may be provided. The transparent basematerial 1033 provided with the coloring layers and the light-blockinglayer is positioned and fixed to the substrate 1001. Note that thecoloring layers and the light-blocking layer are covered with anovercoat layer 1036. In the structure in FIG. 10A, red light, greenlight, and blue light transmit the coloring layers, and thus an imagecan be displayed with the use of pixels of three colors.

FIG. 10B illustrates an example in which, as examples of the opticalelements, the coloring layers (the red coloring layer 1034R, the greencoloring layer 1034G, and the blue coloring layer 1034B) are providedbetween the gate insulating film 1003 and the first interlayerinsulating film 1020. As in this structure, the coloring layers may beprovided between the substrate 1001 and the sealing substrate 1031.

FIG. 11 illustrates an example in which, as examples of the opticalelements, the coloring layers (the red coloring layer 1034R, the greencoloring layer 1034G, and the blue coloring layer 1034B) are providedbetween the first interlayer insulating film 1020 and the secondinterlayer insulating film 1021. As in this structure, the coloringlayers may be provided between the substrate 1001 and the sealingsubstrate 1031.

The above-described display device has a structure in which light isextracted from the substrate 1001 side where the transistors are formed(a bottom-emission structure), but may have a structure in which lightis extracted from the sealing substrate 1031 side (a top-emissionstructure).

Structure Example 3 of Display Device

FIGS. 12A and 12B are each an example of a cross-sectional view of adisplay device having a top emission structure. Note that FIGS. 12A and12B are each a cross-sectional view illustrating the display device ofone embodiment of the present invention, and the driver circuit portion1041, the peripheral portion 1042, and the like, which are illustratedin FIGS. 10A and 10B and FIG. 11, are not illustrated therein.

In this case, as the substrate 1001, a substrate that does not transmitlight can be used. The process up to the step of forming a connectionelectrode which connects the transistor and the anode of thelight-emitting element is performed in a manner similar to that of thedisplay device having a bottom-emission structure. Then, a thirdinterlayer insulating film 1037 is formed to cover an electrode 1022.This insulating film may have a planarization function. The thirdinterlayer insulating film 1037 can be formed by using a materialsimilar to that of the second interlayer insulating film, or can beformed by using any other known materials.

The lower electrodes 1024R, 1024G, and 1024B of the light-emittingelements each function as an anode here, but may function as a cathode.Further, in the case of a display device having a top-emission structureas illustrated in FIGS. 12A and 12B, the lower electrodes 1024R, 1024G,and 1024B preferably have a function of reflecting light. The upperelectrode 1026 is provided over the EL layer 1028. It is preferable thatthe upper electrode 1026 have a function of reflecting light and afunction of transmitting light and that a microcavity structure be usedbetween the upper electrode 1026 and the lower electrodes 1024R, 1024G,and 1024B, in which case the intensity of light having a specificwavelength is increased.

In the case of a top-emission structure as illustrated in FIG. 12A,sealing can be performed with the sealing substrate 1031 on which thecoloring layers (the red coloring layer 1034R, the green coloring layer1034G, and the blue coloring layer 1034B) are provided. The sealingsubstrate 1031 may be provided with the light-blocking layer 1035 whichis positioned between pixels. Note that a light-transmitting substrateis favorably used as the sealing substrate 1031.

FIG. 12A illustrates the structure provided with the light-emittingelements and the coloring layers for the light-emitting elements as anexample; however, the structure is not limited thereto. For example, asshown in FIG. 12B, a structure including the red coloring layer 1034Rand the blue coloring layer 1034B but not including a green coloringlayer may be employed to achieve full color display with the threecolors of red, green, and blue. The structure as illustrated in FIG. 12Awhere the light-emitting elements are provided with the coloring layersis effective to suppress reflection of external light. In contrast, thestructure as illustrated in FIG. 12B where the light-emitting elementsare provided with the red coloring layer and the blue coloring layer andwithout the green coloring layer is effective to reduce powerconsumption because of small energy loss of light emitted from the greenlight-emitting element.

Structure Example 4 of Display Device

Although a display device including sub-pixels of three colors (red,green, and blue) is described above, the number of colors of sub-pixelsmay be four (red, green, blue, and yellow, or red, green, blue, andwhite). FIGS. 13A and 13B, FIG. 14, and FIGS. 15A and 15B illustratestructures of display devices each including the lower electrodes 1024R,1024G, 1024B, and 1024Y. FIGS. 13A and 13B and FIG. 14 each illustrate adisplay device having a structure in which light is extracted from thesubstrate 1001 side on which transistors are formed (bottom-emissionstructure), and FIGS. 15A and 15B each illustrate a display devicehaving a structure in which light is extracted from the sealingsubstrate 1031 side (top-emission structure).

FIG. 13A illustrates an example of a display device in which opticalelements (the coloring layer 1034R, the coloring layer 1034G, thecoloring layer 1034B, and a coloring layer 1034Y) are provided on thetransparent base material 1033. FIG. 13B illustrates an example of adisplay device in which optical elements (the coloring layer 1034R, thecoloring layer 1034G, the coloring layer 1034B, and the coloring layer1034Y) are provided between the gate insulating film 1003 and the firstinterlayer insulating film 1020. FIG. 14 illustrates an example of adisplay device in which optical elements (the coloring layer 1034R, thecoloring layer 1034G, the coloring layer 1034B, and the coloring layer1034Y) are provided between the first interlayer insulating film 1020and the second interlayer insulating film 1021.

The coloring layer 1034R transmits red light, the coloring layer 1034Gtransmits green light, and the coloring layer 1034B transmits bluelight. The coloring layer 1034Y transmits yellow light or transmitslight of a plurality of colors selected from blue, green, yellow, andred. When the coloring layer 1034Y can transmit light of a plurality ofcolors selected from blue, green, yellow, and red, light released fromthe coloring layer 1034Y may be white light. Since the light-emittingelement which transmits yellow or white light has high light emissionefficiency, the display device including the coloring layer 1034Y canhave lower power consumption.

In the top-emission display devices illustrated in FIGS. 15A and 15B, alight-emitting element including the lower electrode 1024Y preferablyhas a microcavity structure between the upper electrode 1026 and thelower electrodes 1024R, 1024G, 1024B, and 1024Y as in the display deviceillustrated in FIG. 12A. In the display device illustrated in FIG. 15A,sealing can be performed with the sealing substrate 1031 on which thecoloring layers (the red coloring layer 1034R, the green coloring layer1034G, the blue coloring layer 1034B, and the yellow coloring layer1034Y) are provided.

Light emitted through the microcavity and the yellow coloring layer1034Y has an emission spectrum in a yellow region. Since yellow is acolor with a high luminosity factor, a light-emitting element emittingyellow light has high light emission efficiency. Therefore, the displaydevice of FIG. 15A can reduce power consumption.

FIG. 15A illustrates the structure provided with the light-emittingelements and the coloring layers for the light-emitting elements as anexample; however, the structure is not limited thereto. For example, asshown in FIG. 15B, a structure including the red coloring layer 1034R,the green coloring layer 1034G, and the blue coloring layer 1034B butnot including a yellow coloring layer may be employed to achieve fullcolor display with the four colors of red, green, blue, and yellow or ofred, green, blue, and white. The structure as illustrated in FIG. 15Awhere the light-emitting elements are provided with the coloring layersis effective to suppress reflection of external light. In contrast, thestructure as illustrated in FIG. 15B where the light-emitting elementsare provided with the red coloring layer, the green coloring layer, andthe blue coloring layer and without the yellow coloring layer iseffective to reduce power consumption because of small energy loss oflight emitted from the yellow or white light-emitting element.

Structure Example 5 of Display Device

Next, a display device of another embodiment of the present invention isdescribed with reference to FIG. 16. FIG. 16 is a cross-sectional viewtaken along the dashed-dotted line A-B and the dashed-dotted line C-D inFIG. 9A. Note that in FIG. 16, portions having functions similar tothose of portions in FIG. 9B are given the same reference numerals as inFIG. 9B, and a detailed description of the portions is omitted.

The display device 600 in FIG. 16 includes a sealing layer 607 a, asealing layer 607 b, and a sealing layer 607 c in a region 607surrounded by the element substrate 610, the sealing substrate 604, andthe sealant 605. For one or more of the sealing layer 607 a, the sealinglayer 607 b, and the sealing layer 607 c, a resin such as a polyvinylchloride (PVC) based resin, an acrylic-based resin, a polyimide-basedresin, an epoxy-based resin, a silicone-based resin, a polyvinyl butyral(PVB) based resin, or an ethylene vinyl acetate (EVA) based resin can beused. Alternatively, an inorganic material such as silicon oxide,silicon oxynitride, silicon nitride oxide, silicon nitride, aluminumoxide, or aluminum nitride can be used. The formation of the sealinglayers 607 a, 607 b, and 607 c can prevent deterioration of thelight-emitting element 618 due to impurities such as water, which ispreferable. In the case where the sealing layers 607 a, 607 b, and 607 care formed, the sealant 605 is not necessarily provided.

Alternatively, any one or two of the sealing layers 607 a, 607 b, and607 c may be provided or four or more sealing layers may be formed. Whenthe sealing layer has a multilayer structure, the impurities such aswater can be effectively prevented from entering the light-emittingelement 618 which is inside the display device from the outside of thedisplay device 600. In the case where the sealing layer has a multilayerstructure, a resin and an organic material are preferably stacked.

Structure Example 6 of Display Device

Although the display devices in the structure examples 1 to 4 in thisembodiment each have a structure including optical elements, oneembodiment of the present invention does not necessarily include anoptical element.

FIGS. 17A and 17B each illustrate a display device having a structure inwhich light is extracted from the sealing substrate 1031 side (atop-emission display device). FIG. 17A illustrates an example of adisplay device including a light-emitting layer 1028R, a light-emittinglayer 1028G, and a light-emitting layer 1028B. FIG. 17B illustrates anexample of a display device including a light-emitting layer 1028R, alight-emitting layer 1028G, a light-emitting layer 1028B, and alight-emitting layer 1028Y.

The light-emitting layer 1028R has a function of exhibiting red light,the light-emitting layer 1028G has a function of exhibiting green light,and the light-emitting layer 1028B has a function of exhibiting bluelight. The light-emitting layer 1028Y has a function of exhibitingyellow light or a function of exhibiting light of a plurality of colorsselected from blue, green, and red. The light-emitting layer 1028Y mayexhibit whit light. Since the light-emitting element which exhibitsyellow or white light has high light emission efficiency, the displaydevice including the light-emitting layer 1028Y can have lower powerconsumption.

Each of the display devices in FIGS. 17A and 17B does not necessarilyinclude coloring layers serving as optical elements because EL layersexhibiting lights of different colors are included in sub-pixels.

For the sealing layer 1029, a resin such as a polyvinyl chloride (PVC)based resin, an acrylic-based resin, a polyimide-based resin, anepoxy-based resin, a silicone-based resin, a polyvinyl butyral (PVB)based resin, or an ethylene vinyl acetate (EVA) based resin can be used.Alternatively, an inorganic material such as silicon oxide, siliconoxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, oraluminum nitride can be used. The formation of the sealing layer 1029can prevent deterioration of the light-emitting element due toimpurities such as water, which is preferable.

Alternatively, the sealing layer 1029 may have a single-layer ortwo-layer structure, or four or more sealing layers may be formed as thesealing layer 1029. When the sealing layer has a multilayer structure,the impurities such as water can be effectively prevented from enteringthe inside of the display device from the outside of the display device.In the case where the sealing layer has a multilayer structure, a resinand an organic material are preferably stacked.

Note that the sealing substrate 1031 has a function of protecting thelight-emitting element. Thus, for the sealing substrate 1031, a flexiblesubstrate or a film can be used.

Note that the structures described in this embodiment can be combined asappropriate with any of the other structures in this embodiment and theother embodiments.

Embodiment 5

In this embodiment, a display device including a light-emitting elementof one embodiment of the present invention will be described withreference to FIGS. 20A and 20B, FIGS. 21A and 21B, and FIGS. 22A and22B.

FIG. 20A is a block diagram illustrating the display device of oneembodiment of the present invention, and FIG. 20B is a circuit diagramillustrating a pixel circuit of the display device of one embodiment ofthe present invention.

<Description of Display Device>

The display device illustrated in FIG. 20A includes a region includingpixels of display elements (the region is hereinafter referred to as apixel portion 802), a circuit portion provided outside the pixel portion802 and including circuits for driving the pixels (the portion ishereinafter referred to as a driver circuit portion 804), circuitshaving a function of protecting elements (the circuits are hereinafterreferred to as protection circuits 806), and a terminal portion 807.Note that the protection circuits 806 are not necessarily provided.

Apart or the whole of the driver circuit portion 804 is preferablyformed over a substrate over which the pixel portion 802 is formed, inwhich case the number of components and the number of terminals can bereduced. When a part or the whole of the driver circuit portion 804 isnot formed over the substrate over which the pixel portion 802 isformed, the part or the whole of the driver circuit portion 804 can bemounted by COG or tape automated bonding (TAB).

The pixel portion 802 includes a plurality of circuits for drivingdisplay elements arranged in X rows (X is a natural number of 2 or more)and Y columns (Y is a natural number of 2 or more) (such circuits arehereinafter referred to as pixel circuits 801). The driver circuitportion 804 includes driver circuits such as a circuit for supplying asignal (scan signal) to select a pixel (the circuit is hereinafterreferred to as a scan line driver circuit 804 a) and a circuit forsupplying a signal (data signal) to drive a display element in a pixel(the circuit is hereinafter referred to as a signal line driver circuit804 b).

The scan line driver circuit 804 a includes a shift register or thelike. Through the terminal portion 807, the scan line driver circuit 804a receives a signal for driving the shift register and outputs a signal.For example, the scan line driver circuit 804 a receives a start pulsesignal, a clock signal, or the like and outputs a pulse signal. The scanline driver circuit 804 a has a function of controlling the potentialsof wirings supplied with scan signals (such wirings are hereinafterreferred to as scan lines GL_1 to GL_X). Note that a plurality of scanline driver circuits 804 a may be provided to control the scan linesGL_1 to GL_X separately. Alternatively, the scan line driver circuit 804a has a function of supplying an initialization signal. Without beinglimited thereto, the scan line driver circuit 804 a can supply anothersignal.

The signal line driver circuit 804 b includes a shift register or thelike. The signal line driver circuit 804 b receives a signal (imagesignal) from which a data signal is derived, as well as a signal fordriving the shift register, through the terminal portion 807. The signalline driver circuit 804 b has a function of generating a data signal tobe written to the pixel circuit 801 which is based on the image signal.In addition, the signal line driver circuit 804 b has a function ofcontrolling output of a data signal in response to a pulse signalproduced by input of a start pulse signal, a clock signal, or the like.Furthermore, the signal line driver circuit 804 b has a function ofcontrolling the potentials of wirings supplied with data signals (suchwirings are hereinafter referred to as data lines DL_1 to DL_Y).Alternatively, the signal line driver circuit 804 b has a function ofsupplying an initialization signal. Without being limited thereto, thesignal line driver circuit 804 b can supply another signal.

The signal line driver circuit 804 b includes a plurality of analogswitches or the like, for example. The signal line driver circuit 804 bcan output, as the data signals, signals obtained by time-dividing theimage signal by sequentially turning on the plurality of analogswitches. The signal line driver circuit 804 b may include a shiftregister or the like.

A pulse signal and a data signal are input to each of the plurality ofpixel circuits 801 through one of the plurality of scan lines GLsupplied with scan signals and one of the plurality of data lines DLsupplied with data signals, respectively. Writing and holding of thedata signal to and in each of the plurality of pixel circuits 801 arecontrolled by the scan line driver circuit 804 a. For example, to thepixel circuit 801 in the m-th row and the n-th column (m is a naturalnumber of less than or equal to X, and n is a natural number of lessthan or equal to Y), a pulse signal is input from the scan line drivercircuit 804 a through the scan line GL_m, and a data signal is inputfrom the signal line driver circuit 804 b through the data line DL_n inaccordance with the potential of the scan line GL_m.

The protection circuit 806 shown in FIG. 20A is connected to, forexample, the scan line GL between the scan line driver circuit 804 a andthe pixel circuit 801. Alternatively, the protection circuit 806 isconnected to the data line DL between the signal line driver circuit 804b and the pixel circuit 801. Alternatively, the protection circuit 806can be connected to a wiring between the scan line driver circuit 804 aand the terminal portion 807. Alternatively, the protection circuit 806can be connected to a wiring between the signal line driver circuit 804b and the terminal portion 807. Note that the terminal portion 807 meansa portion having terminals for inputting power, control signals, andimage signals to the display device from external circuits.

The protection circuit 806 is a circuit that electrically connects awiring connected to the protection circuit to another wiring when apotential out of a certain range is applied to the wiring connected tothe protection circuit.

As illustrated in FIG. 20A, the protection circuits 806 are provided forthe pixel portion 802 and the driver circuit portion 804, so that theresistance of the display device to overcurrent generated byelectrostatic discharge (ESD) or the like can be improved. Note that theconfiguration of the protection circuits 806 is not limited to that, andfor example, a configuration in which the protection circuits 806 areconnected to the scan line driver circuit 804 a or a configuration inwhich the protection circuits 806 are connected to the signal linedriver circuit 804 b may be employed. Alternatively, the protectioncircuits 806 may be configured to be connected to the terminal portion807.

In FIG. 20A, an example in which the driver circuit portion 804 includesthe scan line driver circuit 804 a and the signal line driver circuit804 b is shown; however, the structure is not limited thereto. Forexample, only the scan line driver circuit 804 a may be formed and aseparately prepared substrate where a signal line driver circuit isformed (e.g., a driver circuit substrate formed with a single crystalsemiconductor film or a polycrystalline semiconductor film) may bemounted.

Structure Example of Pixel Circuit

Each of the plurality of pixel circuits 801 in FIG. 20A can have astructure illustrated in FIG. 20B, for example.

The pixel circuit 801 illustrated in FIG. 20B includes transistors 852and 854, a capacitor 862, and a light-emitting element 872.

One of a source electrode and a drain electrode of the transistor 852 iselectrically connected to a wiring to which a data signal is supplied (adata line DL_n). A gate electrode of the transistor 852 is electricallyconnected to a wiring to which a gate signal is supplied (a scan lineGL_m).

The transistor 852 has a function of controlling whether to write a datasignal.

One of a pair of electrodes of the capacitor 862 is electricallyconnected to a wiring to which a potential is supplied (hereinafterreferred to as a potential supply line VL_a), and the other iselectrically connected to the other of the source electrode and thedrain electrode of the transistor 852.

The capacitor 862 functions as a storage capacitor for storing writtendata.

One of a source electrode and a drain electrode of the transistor 854 iselectrically connected to the potential supply line VL_a. Furthermore, agate electrode of the transistor 854 is electrically connected to theother of the source electrode and the drain electrode of the transistor852.

One of an anode and a cathode of the light-emitting element 872 iselectrically connected to a potential supply line VL_b, and the other iselectrically connected to the other of the source electrode and thedrain electrode of the transistor 854.

As the light-emitting element 872, any of the light-emitting elementsdescribed in Embodiments 1 to 3 can be used.

Note that a high power supply potential VDD is supplied to one of thepotential supply line VL_a and the potential supply line VL_b, and a lowpower supply potential VSS is supplied to the other.

In the display device including the pixel circuits 801 in FIG. 20B, thepixel circuits 801 are sequentially selected row by row by the scan linedriver circuit 804 a in FIG. 20A, for example, whereby the transistors852 are turned on and a data signal is written.

When the transistors 852 are turned off, the pixel circuits 801 in whichthe data has been written are brought into a holding state. Furthermore,the amount of current flowing between the source electrode and the drainelectrode of the transistor 854 is controlled in accordance with thepotential of the written data signal. The light-emitting element 872emits light with a luminance corresponding to the amount of flowingcurrent. This operation is sequentially performed row by row; thus, animage is displayed.

Alternatively, the pixel circuit can have a function of compensatingvariation in threshold voltages or the like of a transistor. FIGS. 21Aand 21B and FIGS. 22A and 22B illustrate examples of the pixel circuit.

The pixel circuit illustrated in FIG. 21A includes six transistors(transistors 303_1 to 303_6), a capacitor 304, and a light-emittingelement 305. The pixel circuit illustrated in FIG. 21A is electricallyconnected to wirings 301_1 to 301_5 and wirings 302_1 and 302_2. Notethat as the transistors 303_1 to 303_6, for example, p-channeltransistors can be used.

The pixel circuit shown in FIG. 21B has a configuration in which atransistor 303_7 is added to the pixel circuit shown in FIG. 21A. Thepixel circuit illustrated in FIG. 21B is electrically connected towirings 301_6 and 301_7. The wirings 301_5 and 301_6 may be electricallyconnected to each other. Note that as the transistor 303_7, for example,a p-channel transistor can be used.

The pixel circuit shown in FIG. 22A includes six transistors(transistors 308_1 to 308_6), the capacitor 304, and the light-emittingelement 305. The pixel circuit illustrated in FIG. 22A is electricallyconnected to wirings 306_1 to 306_3 and wirings 307_1 to 307_3. Thewirings 306_1 and 306_3 may be electrically connected to each other.Note that as the transistors 308_1 to 308_6, for example, p-channeltransistors can be used.

The pixel circuit illustrated in FIG. 22B includes two transistors(transistors 309_1 and 309_2), two capacitors (capacitors 304_1 and304_2), and the light-emitting element 305. The pixel circuitillustrated in FIG. 22B is electrically connected to wirings 311_1 to311_3 and wirings 312_1 and 312_2. With the configuration of the pixelcircuit illustrated in FIG. 22B, the pixel circuit can be driven by avoltage inputting current driving method (also referred to as CVCC).Note that as the transistors 309_1 and 309_2, for example, p-channeltransistors can be used.

A light-emitting element of one embodiment of the present invention canbe used for an active matrix method in which an active element isincluded in a pixel of a display device or a passive matrix method inwhich an active element is not included in a pixel of a display device.

In the active matrix method, as an active element (a non-linearelement), not only a transistor but also a variety of active elements(non-linear elements) can be used. For example, a metal insulator metal(MIM), a thin film diode (TFD), or the like can also be used. Sincethese elements can be formed with a smaller number of manufacturingsteps, manufacturing cost can be reduced or yield can be improved.Alternatively, since the size of these elements is small, the apertureratio can be improved, so that power consumption can be reduced andhigher luminance can be achieved.

As a method other than the active matrix method, the passive matrixmethod in which an active element (a non-linear element) is not used canalso be used. Since an active element (a non-linear element) is notused, the number of manufacturing steps is small, so that manufacturingcost can be reduced or yield can be improved. Alternatively, since anactive element (a non-linear element) is not used, the aperture ratiocan be improved, so that power consumption can be reduced or higherluminance can be achieved, for example.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 6

In this embodiment, a display device including a light-emitting elementof one embodiment of the present invention and an electronic device inwhich the display device is provided with an input device will bedescribed with reference to FIGS. 23A and 23B, FIGS. 24A to 24C, FIGS.25A and 25B, FIGS. 26A and 26B, and FIG. 27.

<Description 1 of Touch Panel>

In this embodiment, a touch panel 2000 including a display device and aninput device will be described as an example of an electronic device. Inaddition, an example in which a touch sensor is used as an input devicewill be described.

FIGS. 23A and 23B are perspective views of the touch panel 2000. Notethat FIGS. 23A and 23B illustrate only main components of the touchpanel 2000 for simplicity.

The touch panel 2000 includes a display device 2501 and a touch sensor2595 (see FIG. 23B). The touch panel 2000 also includes a substrate2510, a substrate 2570, and a substrate 2590. The substrate 2510, thesubstrate 2570, and the substrate 2590 each have flexibility. Note thatone or all of the substrates 2510, 2570, and 2590 may be inflexible.

The display device 2501 includes a plurality of pixels over thesubstrate 2510 and a plurality of wirings 2511 through which signals aresupplied to the pixels. The plurality of wirings 2511 are led to aperipheral portion of the substrate 2510, and parts of the plurality ofwirings 2511 form a terminal 2519. The terminal 2519 is electricallyconnected to an FPC 2509(1). The plurality of wirings 2511 can supplysignals from a signal line driver circuit 2503 s(1) to the plurality ofpixels.

The substrate 2590 includes the touch sensor 2595 and a plurality ofwirings 2598 electrically connected to the touch sensor 2595. Theplurality of wirings 2598 are led to a peripheral portion of thesubstrate 2590, and parts of the plurality of wirings 2598 form aterminal. The terminal is electrically connected to an FPC 2509(2). Notethat in FIG. 23B, electrodes, wirings, and the like of the touch sensor2595 provided on the back side of the substrate 2590 (the side facingthe substrate 2510) are indicated by solid lines for clarity.

As the touch sensor 2595, a capacitive touch sensor can be used.Examples of the capacitive touch sensor are a surface capacitive touchsensor and a projected capacitive touch sensor.

Examples of the projected capacitive touch sensor are a self capacitivetouch sensor and a mutual capacitive touch sensor, which differ mainlyin the driving method. The use of a mutual capacitive type is preferablebecause multiple points can be sensed simultaneously.

Note that the touch sensor 2595 illustrated in FIG. 23B is an example ofusing a projected capacitive touch sensor.

Note that a variety of sensors that can sense approach or contact of asensing target such as a finger can be used as the touch sensor 2595.

The projected capacitive touch sensor 2595 includes electrodes 2591 andelectrodes 2592. The electrodes 2591 are electrically connected to anyof the plurality of wirings 2598, and the electrodes 2592 areelectrically connected to any of the other wirings 2598.

The electrodes 2592 each have a shape of a plurality of quadranglesarranged in one direction with one corner of a quadrangle connected toone corner of another quadrangle as illustrated in FIGS. 23A and 23B.

The electrodes 2591 each have a quadrangular shape and are arranged in adirection intersecting with the direction in which the electrodes 2592extend.

A wiring 2594 electrically connects two electrodes 2591 between whichthe electrode 2592 is positioned. The intersecting area of the electrode2592 and the wiring 2594 is preferably as small as possible. Such astructure allows a reduction in the area of a region where theelectrodes are not provided, reducing variation in transmittance. As aresult, variation in luminance of light passing through the touch sensor2595 can be reduced.

Note that the shapes of the electrodes 2591 and the electrodes 2592 arenot limited thereto and can be any of a variety of shapes. For example,a structure may be employed in which the plurality of electrodes 2591are arranged so that gaps between the electrodes 2591 are reduced asmuch as possible, and the electrodes 2592 are spaced apart from theelectrodes 2591 with an insulating layer interposed therebetween to haveregions not overlapping with the electrodes 2591. In this case, it ispreferable to provide, between two adjacent electrodes 2592, a dummyelectrode electrically insulated from these electrodes because the areaof regions having different transmittances can be reduced.

<Description of Display Device>

Next, the display device 2501 will be described in detail with referenceto FIG. 24A. FIG. 24A corresponds to a cross-sectional view taken alongdashed-dotted line X1-X2 in FIG. 23B.

The display device 2501 includes a plurality of pixels arranged in amatrix. Each of the pixels includes a display element and a pixelcircuit for driving the display element.

In the following description, an example of using a light-emittingelement that emits white light as a display element will be described;however, the display element is not limited to such an element. Forexample, light-emitting elements that emit light of different colors maybe included so that the light of different colors can be emitted fromadjacent pixels.

For the substrate 2510 and the substrate 2570, for example, a flexiblematerial with a vapor permeability of lower than or equal to 1×10⁻⁵g·m⁻²·day⁻¹, preferably lower than or equal to 1×10⁻⁶ g·m⁻²·day⁻¹ can befavorably used. Alternatively, materials whose thermal expansioncoefficients are substantially equal to each other are preferably usedfor the substrate 2510 and the substrate 2570. For example, thecoefficients of linear expansion of the materials are preferably lowerthan or equal to 1×10⁻³/K, further preferably lower than or equal to5×10⁻⁵/K, and still further preferably lower than or equal to 1×10⁻⁵/K.

Note that the substrate 2510 is a stacked body including an insulatinglayer 2510 a for preventing impurity diffusion into the light-emittingelement, a flexible substrate 2510 b, and an adhesive layer 2510 c forattaching the insulating layer 2510 a and the flexible substrate 2510 bto each other. The substrate 2570 is a stacked body including aninsulating layer 2570 a for preventing impurity diffusion into thelight-emitting element, a flexible substrate 2570 b, and an adhesivelayer 2570 c for attaching the insulating layer 2570 a and the flexiblesubstrate 2570 b to each other.

For the adhesive layer 2510 c and the adhesive layer 2570 c, forexample, polyester, polyolefin, polyamide (e.g., nylon, aramid),polyimide, polycarbonate, or acrylic, urethane, or epoxy can be used.Alternatively, a material that includes a resin having a siloxane bondcan be used.

A sealing layer 2560 is provided between the substrate 2510 and thesubstrate 2570. The sealing layer 2560 preferably has a refractive indexhigher than that of air. In the case where light is extracted to thesealing layer 2560 side as illustrated in FIG. 24A, the sealing layer2560 can also serve as an optical adhesive layer.

A sealant may be formed in the peripheral portion of the sealing layer2560. With the use of the sealant, a light-emitting element 2550R can beprovided in a region surrounded by the substrate 2510, the substrate2570, the sealing layer 2560, and the sealant. Note that an inert gas(such as nitrogen and argon) may be used instead of the sealing layer2560. A drying agent may be provided in the inert gas so as to adsorbmoisture or the like. Alternatively, a resin such as acrylic or epoxymay be used instead of the sealing layer 2560. An epoxy-based resin or aglass frit is preferably used as the sealant. As a material used for thesealant, a material which is impermeable to moisture and oxygen ispreferably used.

The display device 2501 includes a pixel 2502R. The pixel 2502R includesa light-emitting module 2580R.

The pixel 2502R includes the light-emitting element 2550R and atransistor 2502 t that can supply electric power to the light-emittingelement 2550R. Note that the transistor 2502 t functions as part of thepixel circuit. The light-emitting module 2580R includes thelight-emitting element 2550R and a coloring layer 2567R.

The light-emitting element 2550R includes a lower electrode, an upperelectrode, and an EL layer between the lower electrode and the upperelectrode. As the light-emitting element 2550R, any of thelight-emitting elements described in Embodiments 1 to 3 can be used.

A microcavity structure may be employed between the lower electrode andthe upper electrode so as to increase the intensity of light having aspecific wavelength.

In the case where the sealing layer 2560 is provided on the lightextraction side, the sealing layer 2560 is in contact with thelight-emitting element 2550R and the coloring layer 2567R.

The coloring layer 2567R is positioned in a region overlapping with thelight-emitting element 2550R. Accordingly, part of light emitted fromthe light-emitting element 2550R passes through the coloring layer 2567Rand is emitted to the outside of the light-emitting module 2580R asindicated by an arrow in FIG. 24A.

The display device 2501 includes a light-blocking layer 2567BM on thelight extraction side. The light-blocking layer 2567BM is provided so asto surround the coloring layer 2567R.

The coloring layer 2567R is a coloring layer having a function oftransmitting light in a particular wavelength range. For example, acolor filter for transmitting light in a red wavelength range, a colorfilter for transmitting light in a green wavelength range, a colorfilter for transmitting light in a blue wavelength range, a color filterfor transmitting light in a yellow wavelength range, or the like can beused. Each color filter can be formed with any of various materials by aprinting method, an inkjet method, an etching method using aphotolithography technique, or the like.

An insulating layer 2521 is provided in the display device 2501. Theinsulating layer 2521 covers the transistor 2502 t. Note that theinsulating layer 2521 has a function of covering unevenness caused bythe pixel circuit. The insulating layer 2521 may have a function ofsuppressing impurity diffusion. This can prevent the reliability of thetransistor 2502 t or the like from being lowered by impurity diffusion.

The light-emitting element 2550R is formed over the insulating layer2521. A partition 2528 is provided so as to overlap with an end portionof the lower electrode of the light-emitting element 2550R. Note that aspacer for controlling the distance between the substrate 2510 and thesubstrate 2570 may be formed over the partition 2528.

A scan line driver circuit 2503 g(1) includes a transistor 2503 t and acapacitor 2503 c. Note that the driver circuit can be formed in the sameprocess and over the same substrate as those of the pixel circuits.

The wirings 2511 through which signals can be supplied are provided overthe substrate 2510. The terminal 2519 is provided over the wirings 2511.The FPC 2509(1) is electrically connected to the terminal 2519. The FPC2509(1) has a function of supplying a video signal, a clock signal, astart signal, a reset signal, or the like. Note that the FPC 2509(1) maybe provided with a PWB.

In the display device 2501, transistors with any of a variety ofstructures can be used. FIG. 24A illustrates an example of usingbottom-gate transistors; however, the present invention is not limitedto this example, and top-gate transistors may be used in the displaydevice 2501 as illustrated in FIG. 24B.

In addition, there is no particular limitation on the polarity of thetransistor 2502 t and the transistor 2503 t. For these transistors,n-channel and p-channel transistors may be used, or either n-channeltransistors or p-channel transistors may be used, for example.Furthermore, there is no particular limitation on the crystallinity of asemiconductor film used for the transistors 2502 t and 2503 t. Forexample, an amorphous semiconductor film or a crystalline semiconductorfilm may be used. Examples of semiconductor materials include Group 14semiconductors (e.g., a semiconductor including silicon), compoundsemiconductors (including oxide semiconductors), organic semiconductors,and the like. An oxide semiconductor that has an energy gap of 2 eV ormore, preferably 2.5 eV or more, further preferably 3 eV or more ispreferably used for one of the transistors 2502 t and 2503 t or both, sothat the off-state current of the transistors can be reduced. Examplesof the oxide semiconductors include an In—Ga oxide, an In-M-Zn oxide (Mrepresents Al, Ga, Y, Zr, La, Ce, Sn, Hf, or Nd), and the like.

<Description of Touch Sensor>

Next, the touch sensor 2595 will be described in detail with referenceto FIG. 24C. FIG. 24C corresponds to a cross-sectional view taken alongdashed-dotted line X3-X4 in FIG. 23B.

The touch sensor 2595 includes the electrodes 2591 and the electrodes2592 provided in a staggered arrangement on the substrate 2590, aninsulating layer 2593 covering the electrodes 2591 and the electrodes2592, and the wiring 2594 that electrically connects the adjacentelectrodes 2591 to each other.

The electrodes 2591 and the electrodes 2592 are formed using alight-transmitting conductive material. As a light-transmittingconductive material, a conductive oxide such as indium oxide, indium tinoxide, indium zinc oxide, zinc oxide, or zinc oxide to which gallium isadded can be used. Note that a film including graphene may be used aswell. The film including graphene can be formed, for example, byreducing a film containing graphene oxide. As a reducing method, amethod with application of heat or the like can be employed.

The electrodes 2591 and the electrodes 2592 may be formed by, forexample, depositing a light-transmitting conductive material on thesubstrate 2590 by a sputtering method and then removing an unnecessaryportion by any of various pattern forming techniques such asphotolithography.

Examples of a material for the insulating layer 2593 are a resin such asan acrylic resin or an epoxy resin, a resin having a siloxane bond, andan inorganic insulating material such as silicon oxide, siliconoxynitride, or aluminum oxide.

Openings reaching the electrodes 2591 are formed in the insulating layer2593, and the wiring 2594 electrically connects the adjacent electrodes2591. Alight-transmitting conductive material can be favorably used asthe wiring 2594 because the aperture ratio of the touch panel can beincreased. Moreover, a material with higher conductivity than theconductivities of the electrodes 2591 and 2592 can be favorably used forthe wiring 2594 because electric resistance can be reduced.

One electrode 2592 extends in one direction, and a plurality ofelectrodes 2592 are provided in the form of stripes. The wiring 2594intersects with the electrode 2592.

Adjacent electrodes 2591 are provided with one electrode 2592 providedtherebetween. The wiring 2594 electrically connects the adjacentelectrodes 2591.

Note that the plurality of electrodes 2591 are not necessarily arrangedin the direction orthogonal to one electrode 2592 and may be arranged tointersect with one electrode 2592 at an angle of more than 0 degrees andless than 90 degrees.

The wiring 2598 is electrically connected to any of the electrodes 2591and 2592. Part of the wiring 2598 functions as a terminal. For thewiring 2598, a metal material such as aluminum, gold, platinum, silver,nickel, titanium, tungsten, chromium, molybdenum, iron, cobalt, copper,or palladium or an alloy material containing any of these metalmaterials can be used.

Note that an insulating layer that covers the insulating layer 2593 andthe wiring 2594 may be provided to protect the touch sensor 2595.

A connection layer 2599 electrically connects the wiring 2598 to the FPC2509(2).

As the connection layer 2599, any of various anisotropic conductivefilms (ACF), anisotropic conductive pastes (ACP), and the like can beused.

<Description 2 of Touch Panel>

Next, the touch panel 2000 will be described in detail with reference toFIG. 25A. FIG. 25A corresponds to a cross-sectional view taken alongdashed-dotted line X5-X6 in FIG. 23A.

In the touch panel 2000 illustrated in FIG. 25A, the display device 2501described with reference to FIG. 24A and the touch sensor 2595 describedwith reference to FIG. 24C are attached to each other.

The touch panel 2000 illustrated in FIG. 25A includes an adhesive layer2597 and an anti-reflective layer 2567 p in addition to the componentsdescribed with reference to FIGS. 24A and 24C.

The adhesive layer 2597 is provided in contact with the wiring 2594.Note that the adhesive layer 2597 attaches the substrate 2590 to thesubstrate 2570 so that the touch sensor 2595 overlaps with the displaydevice 2501. The adhesive layer 2597 preferably has a light-transmittingproperty. A heat curable resin or an ultraviolet curable resin can beused for the adhesive layer 2597. For example, an acrylic resin, aurethane-based resin, an epoxy-based resin, or a siloxane-based resincan be used.

The anti-reflective layer 2567 p is positioned in a region overlappingwith pixels. As the anti-reflective layer 2567 p, a circularlypolarizing plate can be used, for example.

Next, a touch panel having a structure different from that illustratedin FIG. 25A will be described with reference to FIG. 25B.

FIG. 25B is a cross-sectional view of a touch panel 2001. The touchpanel 2001 illustrated in FIG. 25B differs from the touch panel 2000illustrated in FIG. 25A in the position of the touch sensor 2595relative to the display device 2501. Different parts are described indetail below, and the above description of the touch panel 2000 isreferred to for the other similar parts.

The coloring layer 2567R is positioned in a region overlapping with thelight-emitting element 2550R. The light-emitting element 2550Rillustrated in FIG. 25B emits light to the side where the transistor2502 t is provided. Accordingly, part of light emitted from thelight-emitting element 2550R passes through the coloring layer 2567R andis emitted to the outside of the light-emitting module 2580R asindicated by an arrow in FIG. 25B.

The touch sensor 2595 is provided on the substrate 2510 side of thedisplay device 2501.

The adhesive layer 2597 is provided between the substrate 2510 and thesubstrate 2590 and attaches the touch sensor 2595 to the display device2501.

As illustrated in FIG. 25A or 25B, light may be emitted from thelight-emitting element through one or both of the substrate 2510 and thesubstrate 2570.

<Description of Method for Driving Touch Panel>

Next, an example of a method for driving a touch panel will be describedwith reference to FIGS. 26A and 26B.

FIG. 26A is a block diagram illustrating the structure of a mutualcapacitive touch sensor. FIG. 26A illustrates a pulse voltage outputcircuit 2601 and a current sensing circuit 2602. Note that in FIG. 26A,six wirings X1 to X6 represent the electrodes 2621 to which a pulsevoltage is applied, and six wirings Y1 to Y6 represent the electrodes2622 that detect changes in current. FIG. 26A also illustratescapacitors 2603 that are each formed in a region where the electrodes2621 and 2622 overlap with each other. Note that functional replacementbetween the electrodes 2621 and 2622 is possible.

The pulse voltage output circuit 2601 is a circuit for sequentiallyapplying a pulse voltage to the wirings X1 to X6. By application of apulse voltage to the wirings X1 to X6, an electric field is generatedbetween the electrodes 2621 and 2622 of the capacitor 2603. When theelectric field between the electrodes is shielded, for example, a changeoccurs in the capacitor 2603 (mutual capacitance). The approach orcontact of a sensing target can be sensed by utilizing this change.

The current sensing circuit 2602 is a circuit for detecting changes incurrent flowing through the wirings Y1 to Y6 that are caused by thechange in mutual capacitance in the capacitor 2603. No change in currentvalue is detected in the wirings Y1 to Y6 when there is no approach orcontact of a sensing target, whereas a decrease in current value isdetected when mutual capacitance is decreased owing to the approach orcontact of a sensing target. Note that an integrator circuit or the likeis used for sensing of current values.

FIG. 26B is a timing chart showing input and output waveforms in themutual capacitive touch sensor illustrated in FIG. 26A. In FIG. 26B,sensing of a sensing target is performed in all the rows and columns inone frame period. FIG. 26B shows a period when a sensing target is notsensed (not touched) and a period when a sensing target is sensed(touched). In FIG. 26B, sensed current values of the wirings Y1 to Y6are shown as the waveforms of voltage values.

A pulse voltage is sequentially applied to the wirings X1 to X6, and thewaveforms of the wirings Y1 to Y6 change in accordance with the pulsevoltage. When there is no approach or contact of a sensing target, thewaveforms of the wirings Y1 to Y6 change in accordance with changes inthe voltages of the wirings X1 to X6. The current value is decreased atthe point of approach or contact of a sensing target and accordingly thewaveform of the voltage value changes.

By detecting a change in mutual capacitance in this manner, the approachor contact of a sensing target can be sensed.

<Description of Sensor Circuit>

Although FIG. 26A illustrates a passive matrix type touch sensor inwhich only the capacitor 2603 is provided at the intersection of wiringsas a touch sensor, an active matrix type touch sensor including atransistor and a capacitor may be used. FIG. 27 illustrates an exampleof a sensor circuit included in an active matrix type touch sensor.

The sensor circuit in FIG. 27 includes the capacitor 2603 andtransistors 2611, 2612, and 2613.

A signal G2 is input to a gate of the transistor 2613. A voltage VRES isapplied to one of a source and a drain of the transistor 2613, and oneelectrode of the capacitor 2603 and a gate of the transistor 2611 areelectrically connected to the other of the source and the drain of thetransistor 2613. One of a source and a drain of the transistor 2611 iselectrically connected to one of a source and a drain of the transistor2612, and a voltage VSS is applied to the other of the source and thedrain of the transistor 2611. A signal G1 is input to a gate of thetransistor 2612, and a wiring ML is electrically connected to the otherof the source and the drain of the transistor 2612. The voltage VSS isapplied to the other electrode of the capacitor 2603.

Next, the operation of the sensor circuit in FIG. 27 will be described.First, a potential for turning on the transistor 2613 is supplied as thesignal G2, and a potential with respect to the voltage VRES is thusapplied to the node n connected to the gate of the transistor 2611.Then, a potential for turning off the transistor 2613 is applied as thesignal G2, whereby the potential of the node n is maintained.

Then, mutual capacitance of the capacitor 2603 changes owing to theapproach or contact of a sensing target such as a finger, andaccordingly the potential of the node n is changed from VRES.

In reading operation, a potential for turning on the transistor 2612 issupplied as the signal G1. A current flowing through the transistor2611, that is, a current flowing through the wiring ML is changed inaccordance with the potential of the node n. By sensing this current,the approach or contact of a sensing target can be sensed.

In each of the transistors 2611, 2612, and 2613, an oxide semiconductorlayer is preferably used as a semiconductor layer in which a channelregion is formed. In particular, such a transistor is preferably used asthe transistor 2613 so that the potential of the node n can be held fora long time and the frequency of operation of resupplying VRES to thenode n (refresh operation) can be reduced.

The structures described in this embodiment can be used in appropriatecombination with any of the structures described in the otherembodiments.

Embodiment 7

In this embodiment, a display module and electronic devices including alight-emitting element of one embodiment of the present invention willbe described with reference to FIG. 28, FIGS. 29A to 29G, FIGS. 30A to30D, and FIGS. 31A and 31B.

<Description of Display Module>

In a display module 8000 in FIG. 28, a touch sensor 8004 connected to anFPC 8003, a display device 8006 connected to an FPC 8005, a frame 8009,a printed board 8010, and a battery 8011 are provided between an uppercover 8001 and a lower cover 8002.

The light-emitting element of one embodiment of the present inventioncan be used for the display device 8006, for example.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the sizes of the touchsensor 8004 and the display device 8006.

The touch sensor 8004 can be a resistive touch sensor or a capacitivetouch sensor and may be formed to overlap with the display device 8006.A counter substrate (sealing substrate) of the display device 8006 canhave a touch sensor function. A photosensor may be provided in eachpixel of the display device 8006 so that an optical touch sensor isobtained.

The frame 8009 protects the display device 8006 and also serves as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed board 8010. The frame 8009 may serve as aradiator plate.

The printed board 8010 has a power supply circuit and a signalprocessing circuit for outputting a video signal and a clock signal. Asa power source for supplying power to the power supply circuit, anexternal commercial power source or the battery 8011 provided separatelymay be used. The battery 8011 can be omitted in the case of using acommercial power source.

The display module 8000 can be additionally provided with a member suchas a polarizing plate, a retardation plate, or a prism sheet.

<Description of Electronic Device>

FIGS. 29A to 29G illustrate electronic devices. These electronic devicescan include a housing 9000, a display portion 9001, a speaker 9003,operation keys 9005 (including a power switch or an operation switch), aconnection terminal 9006, a sensor 9007 (a sensor having a function ofmeasuring or sensing force, displacement, position, speed, acceleration,angular velocity, rotational frequency, distance, light, liquid,magnetism, temperature, chemical substance, sound, time, hardness,electric field, current, voltage, electric power, radiation, flow rate,humidity, gradient, oscillation, odor, or infrared ray), a microphone9008, and the like. In addition, the sensor 9007 may have a function ofmeasuring biological information like a pulse sensor and a finger printsensor.

The electronic devices illustrated in FIGS. 29A to 29G can have avariety of functions, for example, a function of displaying a variety ofdata (a still image, a moving image, a text image, and the like) on thedisplay portion, a touch sensor function, a function of displaying acalendar, date, time, and the like, a function of controlling a processwith a variety of software (programs), a wireless communicationfunction, a function of being connected to a variety of computernetworks with a wireless communication function, a function oftransmitting and receiving a variety of data with a wirelesscommunication function, a function of reading a program or data storedin a memory medium and displaying the program or data on the displayportion, and the like. Note that functions that can be provided for theelectronic devices illustrated in FIGS. 29A to 29G are not limited tothose described above, and the electronic devices can have a variety offunctions. Although not illustrated in FIGS. 29A to 29G, the electronicdevices may include a plurality of display portions. The electronicdevices may have a camera or the like and a function of taking a stillimage, a function of taking a moving image, a function of storing thetaken image in a memory medium (an external memory medium or a memorymedium incorporated in the camera), a function of displaying the takenimage on the display portion, or the like.

The electronic devices illustrated in FIGS. 29A to 29G will be describedin detail below.

FIG. 29A is a perspective view of a portable information terminal 9100.The display portion 9001 of the portable information terminal 9100 isflexible. Therefore, the display portion 9001 can be incorporated alonga bent surface of a bent housing 9000. In addition, the display portion9001 includes a touch sensor, and operation can be performed by touchingthe screen with a finger, a stylus, or the like. For example, when anicon displayed on the display portion 9001 is touched, an applicationcan be started.

FIG. 29B is a perspective view of a portable information terminal 9101.The portable information terminal 9101 functions as, for example, one ormore of a telephone set, a notebook, and an information browsing system.Specifically, the portable information terminal can be used as asmartphone. Note that the speaker 9003, the connection terminal 9006,the sensor 9007, and the like, which are not shown in FIG. 29B, can bepositioned in the portable information terminal 9101 as in the portableinformation terminal 9100 shown in FIG. 29A. The portable informationterminal 9101 can display characters and image information on itsplurality of surfaces. For example, three operation buttons 9050 (alsoreferred to as operation icons, or simply, icons) can be displayed onone surface of the display portion 9001. Furthermore, information 9051indicated by dashed rectangles can be displayed on another surface ofthe display portion 9001. Examples of the information 9051 includedisplay indicating reception of an incoming email, social networkingservice (SNS) message, call, and the like; the title and sender of anemail and SNS message; the date; the time; remaining battery; and thereception strength of an antenna. Instead of the information 9051, theoperation buttons 9050 or the like may be displayed on the positionwhere the information 9051 is displayed.

FIG. 29C is a perspective view of a portable information terminal 9102.The portable information terminal 9102 has a function of displayinginformation on three or more surfaces of the display portion 9001. Here,information 9052, information 9053, and information 9054 are displayedon different surfaces. For example, a user of the portable informationterminal 9102 can see the display (here, the information 9053) with theportable information terminal 9102 put in a breast pocket of his/herclothes. Specifically, a caller's phone number, name, or the like of anincoming call is displayed in a position that can be seen from above theportable information terminal 9102. Thus, the user can see the displaywithout taking out the portable information terminal 9102 from thepocket and decide whether to answer the call.

FIG. 29D is a perspective view of a watch-type portable informationterminal 9200. The portable information terminal 9200 is capable ofexecuting a variety of applications such as mobile phone calls,e-mailing, viewing and editing texts, music reproduction, Internetcommunication, and computer games. The display surface of the displayportion 9001 is bent, and images can be displayed on the bent displaysurface. The portable information terminal 9200 can employ near fieldcommunication that is a communication method based on an existingcommunication standard. In that case, for example, mutual communicationbetween the portable information terminal 9200 and a headset capable ofwireless communication can be performed, and thus hands-free calling ispossible. The portable information terminal 9200 includes the connectionterminal 9006, and data can be directly transmitted to and received fromanother information terminal via a connector. Power charging through theconnection terminal 9006 is possible. Note that the charging operationmay be performed by wireless power feeding without using the connectionterminal 9006.

FIGS. 29E, 29F, and 29G are perspective views of a foldable portableinformation terminal 9201. FIG. 29E is a perspective view illustratingthe portable information terminal 9201 that is opened. FIG. 29F is aperspective view illustrating the portable information terminal 9201that is being opened or being folded. FIG. 29G is a perspective viewillustrating the portable information terminal 9201 that is folded. Theportable information terminal 9201 is highly portable when folded. Whenthe portable information terminal 9201 is opened, a seamless largedisplay region is highly browsable. The display portion 9001 of theportable information terminal 9201 is supported by three housings 9000joined together by hinges 9055. By folding the portable informationterminal 9201 at a connection portion between two housings 9000 with thehinges 9055, the portable information terminal 9201 can be reversiblychanged in shape from an opened state to a folded state. For example,the portable information terminal 9201 can be bent with a radius ofcurvature of greater than or equal to 1 mm and less than or equal to 150mm.

Examples of electronic devices are a television set (also referred to asa television or a television receiver), a monitor of a computer or thelike, a camera such as a digital camera or a digital video camera, adigital photo frame, a mobile phone handset (also referred to as amobile phone or a mobile phone device), a goggle-type display (headmounted display), a portable game machine, a portable informationterminal, an audio reproducing device, and a large-sized game machinesuch as a pachinko machine.

FIG. 30A illustrates an example of a television set. In the televisionset 9300, the display portion 9001 is incorporated into the housing9000. Here, the housing 9000 is supported by a stand 9301.

The television set 9300 illustrated in FIG. 30A can be operated with anoperation switch of the housing 9000 or a separate remote controller9311. The display portion 9001 may include a touch sensor. Thetelevision set 9300 can be operated by touching the display portion 9001with a finger or the like. The remote controller 9311 may be providedwith a display portion for displaying data output from the remotecontroller 9311. With operation keys or a touch panel of the remotecontroller 9311, channels or volume can be controlled and imagesdisplayed on the display portion 9001 can be controlled.

The television set 9300 is provided with a receiver, a modem, or thelike. A general television broadcast can be received with the receiver.When the television set is connected to a communication network with orwithout wires via the modem, one-way (from a transmitter to a receiver)or two-way (between a transmitter and a receiver or between receivers)data communication can be performed.

The electronic device or the lighting device of one embodiment of thepresent invention has flexibility and therefore can be incorporatedalong a curved inside/outside wall surface of a house or a building or acurved interior/exterior surface of a car.

FIG. 30B is an external view of an automobile 9700. FIG. 30C illustratesa driver's seat of the automobile 9700. The automobile 9700 includes acar body 9701, wheels 9702, a dashboard 9703, lights 9704, and the like.The display device, the light-emitting device, or the like of oneembodiment of the present invention can be used in a display portion orthe like of the automobile 9700. For example, the display device, thelight-emitting device, or the like of one embodiment of the presentinvention can be used in display portions 9710 to 9715 illustrated inFIG. 30C.

The display portion 9710 and the display portion 9711 are each a displaydevice provided in an automobile windshield. The display device, thelight-emitting device, or the like of one embodiment of the presentinvention can be a see-through display device, through which theopposite side can be seen, using a light-transmitting conductivematerial for its electrodes and wirings. Such a see-through displayportion 9710 or 9711 does not hinder driver's vision during driving theautomobile 9700. Thus, the display device, the light-emitting device, orthe like of one embodiment of the present invention can be provided inthe windshield of the automobile 9700. Note that in the case where atransistor or the like for driving the display device, thelight-emitting device, or the like is provided, a transistor having alight-transmitting property, such as an organic transistor using anorganic semiconductor material or a transistor using an oxidesemiconductor, is preferably used.

The display portion 9712 is a display device provided on a pillarportion. For example, an image taken by an imaging unit provided in thecar body is displayed on the display portion 9712, whereby the viewhindered by the pillar portion can be compensated. The display portion9713 is a display device provided on the dashboard. For example, animage taken by an imaging unit provided in the car body is displayed onthe display portion 9713, whereby the view hindered by the dashboard canbe compensated. That is, by displaying an image taken by an imaging unitprovided on the outside of the automobile, blind areas can be eliminatedand safety can be increased. Displaying an image to compensate for thearea which a driver cannot see, makes it possible for the driver toconfirm safety easily and comfortably.

FIG. 30D illustrates the inside of a car in which bench seats are usedfor a driver seat and a front passenger seat. A display portion 9721 isa display device provided in a door portion. For example, an image takenby an imaging unit provided in the car body is displayed on the displayportion 9721, whereby the view hindered by the door can be compensated.A display portion 9722 is a display device provided in a steering wheel.A display portion 9723 is a display device provided in the middle of aseating face of the bench seat. Note that the display device can be usedas a seat heater by providing the display device on the seating face orbackrest and by using heat generation of the display device as a heatsource.

The display portion 9714, the display portion 9715, and the displayportion 9722 can provide a variety of kinds of information such asnavigation data, a speedometer, a tachometer, a mileage, a fuel meter, agearshift indicator, and air-condition setting. The content, layout, orthe like of the display on the display portions can be changed freely bya user as appropriate. The information listed above can also bedisplayed on the display portions 9710 to 9713, 9721, and 9723. Thedisplay portions 9710 to 9715 and 9721 to 9723 can also be used aslighting devices. The display portions 9710 to 9715 and 9721 to 9723 canalso be used as heating devices.

Furthermore, the electronic device of one embodiment of the presentinvention may include a secondary battery. It is preferable that thesecondary battery be capable of being charged by non-contact powertransmission.

Examples of the secondary battery include a lithium ion secondarybattery such as a lithium polymer battery using a gel electrolyte(lithium ion polymer battery), a lithium-ion battery, a nickel-hydridebattery, a nickel-cadmium battery, an organic radical battery, alead-acid battery, an air secondary battery, a nickel-zinc battery, anda silver-zinc battery.

The electronic device of one embodiment of the present invention mayinclude an antenna. When a signal is received by the antenna, theelectronic device can display an image, data, or the like on a displayportion. When the electronic device includes a secondary battery, theantenna may be used for contactless power transmission.

A display device 9500 illustrated in FIGS. 31A and 31B includes aplurality of display panels 9501, a hinge 9511, and a bearing 9512. Theplurality of display panels 9501 each include a display region 9502 anda light-transmitting region 9503.

Each of the plurality of display panels 9501 is flexible. Two adjacentdisplay panels 9501 are provided so as to partly overlap with eachother. For example, the light-transmitting regions 9503 of the twoadjacent display panels 9501 can be overlapped each other. A displaydevice having a large screen can be obtained with the plurality ofdisplay panels 9501. The display device is highly versatile because thedisplay panels 9501 can be wound depending on its use.

Moreover, although the display regions 9502 of the adjacent displaypanels 9501 are separated from each other in FIGS. 31A and 31B, withoutlimitation to this structure, the display regions 9502 of the adjacentdisplay panels 9501 may overlap with each other without any space sothat a continuous display region 9502 is obtained, for example.

The electronic devices described in this embodiment each include thedisplay portion for displaying some sort of data. Note that thelight-emitting element of one embodiment of the present invention canalso be used for an electronic device which does not have a displayportion. The structure in which the display portion of the electronicdevice described in this embodiment is flexible and display can beperformed on the bent display surface or the structure in which thedisplay portion of the electronic device is foldable is described as anexample; however, the structure is not limited thereto and a structurein which the display portion of the electronic device is not flexibleand display is performed on a plane portion may be employed.

The structure described in this embodiment can be used in appropriatecombination with the structure described in any of the otherembodiments.

Embodiment 8

In this embodiment, a light-emitting device including the light-emittingelement of one embodiment of the present invention will be describedwith reference to FIGS. 32A to 32C and FIGS. 33A to 33D.

FIG. 32A is a perspective view of a light-emitting device 3000 shown inthis embodiment, and FIG. 32B is a cross-sectional view alongdashed-dotted line E-F in FIG. 32A. Note that in FIG. 32A, somecomponents are illustrated by broken lines in order to avoid complexityof the drawing.

The light-emitting device 3000 illustrated in FIGS. 32A and 32B includesa substrate 3001, a light-emitting element 3005 over the substrate 3001,a first sealing region 3007 provided around the light-emitting element3005, and a second sealing region 3009 provided around the first sealingregion 3007.

Light is emitted from the light-emitting element 3005 through one orboth of the substrate 3001 and a substrate 3003. In FIGS. 32A and 32B, astructure in which light is emitted from the light-emitting element 3005to the lower side (the substrate 3001 side) is illustrated.

As illustrated in FIGS. 32A and 32B, the light-emitting device 3000 hasa double sealing structure in which the light-emitting element 3005 issurrounded by the first sealing region 3007 and the second sealingregion 3009. With the double sealing structure, entry of impurities(e.g., water, oxygen, and the like) from the outside into thelight-emitting element 3005 can be favorably suppressed. Note that it isnot necessary to provide both the first sealing region 3007 and thesecond sealing region 3009. For example, only the first sealing region3007 may be provided.

Note that in FIG. 32B, the first sealing region 3007 and the secondsealing region 3009 are each provided in contact with the substrate 3001and the substrate 3003. However, without limitation to such a structure,for example, one or both of the first sealing region 3007 and the secondsealing region 3009 may be provided in contact with an insulating filmor a conductive film provided on the substrate 3001. Alternatively, oneor both of the first sealing region 3007 and the second sealing region3009 may be provided in contact with an insulating film or a conductivefilm provided on the substrate 3003.

The substrate 3001 and the substrate 3003 can have structures similar tothose of the substrate 200 and the substrate 220 described in Embodiment3, respectively. The light-emitting element 3005 can have a structuresimilar to that of any of the light-emitting elements described in theabove embodiments.

For the first sealing region 3007, a material containing glass (e.g., aglass frit, a glass ribbon, and the like) can be used. For the secondsealing region 3009, a material containing a resin can be used. With theuse of the material containing glass for the first sealing region 3007,productivity and a sealing property can be improved. Moreover, with theuse of the material containing a resin for the second sealing region3009, impact resistance and heat resistance can be improved. However,the materials used for the first sealing region 3007 and the secondsealing region 3009 are not limited to such, and the first sealingregion 3007 may be formed using the material containing a resin and thesecond sealing region 3009 may be formed using the material containingglass.

The glass frit may contain, for example, magnesium oxide, calcium oxide,strontium oxide, barium oxide, cesium oxide, sodium oxide, potassiumoxide, boron oxide, vanadium oxide, zinc oxide, tellurium oxide,aluminum oxide, silicon dioxide, lead oxide, tin oxide, phosphorusoxide, ruthenium oxide, rhodium oxide, iron oxide, copper oxide,manganese dioxide, molybdenum oxide, niobium oxide, titanium oxide,tungsten oxide, bismuth oxide, zirconium oxide, lithium oxide, antimonyoxide, lead borate glass, tin phosphate glass, vanadate glass, orborosilicate glass. The glass frit preferably contains at least one kindof transition metal to absorb infrared light.

As the above glass frits, for example, a frit paste is applied to asubstrate and is subjected to heat treatment, laser light irradiation,or the like. The frit paste contains the glass frit and a resin (alsoreferred to as a binder) diluted by an organic solvent. Note that anabsorber which absorbs light having the wavelength of laser light may beadded to the glass frit. For example, an Nd:YAG laser or a semiconductorlaser is preferably used as the laser. The shape of laser light may becircular or quadrangular.

As the above material containing a resin, for example, materials thatinclude polyester, polyolefin, polyamide (e.g., nylon, aramid),polyimide, polycarbonate, an acrylic resin, urethane, an epoxy resin, ora resin having a siloxane bond can be used.

Note that in the case where the material containing glass is used forone or both of the first sealing region 3007 and the second sealingregion 3009, the material containing glass preferably has a thermalexpansion coefficient close to that of the substrate 3001. With theabove structure, generation of a crack in the material containing glassor the substrate 3001 due to thermal stress can be suppressed.

For example, the following advantageous effect can be obtained in thecase where the material containing glass is used for the first sealingregion 3007 and the material containing a resin is used for the secondsealing region 3009.

The second sealing region 3009 is provided closer to an outer portion ofthe light-emitting device 3000 than the first sealing region 3007 is. Inthe light-emitting device 3000, distortion due to external force or thelike increases toward the outer portion. Thus, the outer portion of thelight-emitting device 3000 where a larger amount of distortion isgenerated, that is, the second sealing region 3009 is sealed using thematerial containing a resin and the first sealing region 3007 providedon an inner side of the second sealing region 3009 is sealed using thematerial containing glass, whereby the light-emitting device 3000 isless likely to be damaged even when distortion due to external force orthe like is generated.

Furthermore, as illustrated in FIG. 32B, a first region 3011 correspondsto the region surrounded by the substrate 3001, the substrate 3003, thefirst sealing region 3007, and the second sealing region 3009. A secondregion 3013 corresponds to the region surrounded by the substrate 3001,the substrate 3003, the light-emitting element 3005, and the firstsealing region 3007.

The first region 3011 and the second region 3013 are preferably filledwith an inert gas such as a rare gas or a nitrogen gas, a resin such asacrylic or epoxy, or the like. Note that for the first region 3011 andthe second region 3013, a reduced pressure state is preferred to anatmospheric pressure state.

FIG. 32C illustrates a modification example of the structure in FIG.32B. FIG. 32C is a cross-sectional view illustrating the modificationexample of the light-emitting device 3000.

FIG. 32C illustrates a structure in which a desiccant 3018 is providedin a recessed portion provided in part of the substrate 3003. The othercomponents are the same as those of the structure illustrated in FIG.32B.

As the desiccant 3018, a substance which adsorbs moisture and the likeby chemical adsorption or a substance which adsorbs moisture and thelike by physical adsorption can be used. Examples of the substance thatcan be used as the desiccant 3018 include alkali metal oxides, alkalineearth metal oxide (e.g., calcium oxide, barium oxide, and the like),sulfate, metal halides, perchlorate, zeolite, silica gel, and the like.

Next, modification examples of the light-emitting device 3000 which isillustrated in FIG. 32B are described with reference to FIGS. 33A to33D. Note that FIGS. 33A to 33D are cross-sectional views illustratingthe modification examples of the light-emitting device 3000 illustratedin FIG. 32B.

In each of the light-emitting devices illustrated in FIGS. 33A to 33D,the second sealing region 3009 is not provided but only the firstsealing region 3007 is provided. Moreover, in each of the light-emittingdevices illustrated in FIGS. 33A to 33D, a region 3014 is providedinstead of the second region 3013 illustrated in FIG. 32B.

For the region 3014, for example, materials that include polyester,polyolefin, polyamide (e.g., nylon or aramid), polyimide, polycarbonate,an acrylic resin, an epoxy resin, urethane, an epoxy resin, or a resinhaving a siloxane bond can be used.

When the above-described material is used for the region 3014, what iscalled a solid-sealing light-emitting device can be obtained.

In the light-emitting device illustrated in FIG. 33B, a substrate 3015is provided on the substrate 3001 side of the light-emitting deviceillustrated in FIG. 33A.

The substrate 3015 has unevenness as illustrated in FIG. 33B. With astructure in which the substrate 3015 having unevenness is provided onthe side through which light emitted from the light-emitting element3005 is extracted, the efficiency of extraction of light from thelight-emitting element 3005 can be improved. Note that instead of thestructure having unevenness and illustrated in FIG. 33B, a substratehaving a function as a diffusion plate may be provided.

In the light-emitting device illustrated in FIG. 33C, light is extractedthrough the substrate 3003 side, unlike in the light-emitting deviceillustrated in FIG. 33A, in which light is extracted through thesubstrate 3001 side.

The light-emitting device illustrated in FIG. 33C includes the substrate3015 on the substrate 3003 side. The other components are the same asthose of the light-emitting device illustrated in FIG. 33B.

In the light-emitting device illustrated in FIG. 33D, the substrate 3003and the substrate 3015 included in the light-emitting device illustratedin FIG. 33C are not provided but a substrate 3016 is provided.

The substrate 3016 includes first unevenness positioned closer to thelight-emitting element 3005 and second unevenness positioned fartherfrom the light-emitting element 3005. With the structure illustrated inFIG. 33D, the efficiency of extraction of light from the light-emittingelement 3005 can be further improved.

Thus, the use of the structure described in this embodiment can providea light-emitting device in which deterioration of a light-emittingelement due to impurities such as moisture and oxygen is suppressed.Alternatively, with the structure described in this embodiment, alight-emitting device having high light extraction efficiency can beobtained.

Note that the structure described in this embodiment can be combinedwith the structure described in any of the other embodiments asappropriate.

Embodiment 9

In this embodiment, examples in which the light-emitting element of oneembodiment of the present invention is used for various lighting devicesand electronic devices will be described with reference to FIGS. 34A to34C and FIG. 35.

An electronic device or a lighting device that has a light-emittingregion with a curved surface can be obtained with the use of thelight-emitting element of one embodiment of the present invention whichis manufactured over a substrate having flexibility.

Furthermore, a light-emitting device to which one embodiment of thepresent invention is applied can also be used for lighting for motorvehicles, examples of which are lighting for a dashboard, a windshield,a ceiling, and the like.

FIG. 34A is a perspective view illustrating one surface of amultifunction terminal 3500, and FIG. 34B is a perspective viewillustrating the other surface of the multifunction terminal 3500. In ahousing 3502 of the multifunction terminal 3500, a display portion 3504,a camera 3506, lighting 3508, and the like are incorporated. Thelight-emitting device of one embodiment of the present invention can beused for the lighting 3508.

The lighting 3508 that includes the light-emitting device of oneembodiment of the present invention functions as a planar light source.Thus, unlike a point light source typified by an LED, the lighting 3508can provide light emission with low directivity. When the lighting 3508and the camera 3506 are used in combination, for example, imaging can beperformed by the camera 3506 with the lighting 3508 lighting orflashing. Because the lighting 3508 functions as a planar light source,a photograph as if taken under natural light can be taken.

Note that the multifunction terminal 3500 illustrated in FIGS. 34A and34B can have a variety of functions as in the electronic devicesillustrated in FIGS. 29A to 29G.

The housing 3502 can include a speaker, a sensor (a sensor having afunction of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared rays), amicrophone, and the like. When a detection device including a sensor fordetecting inclination, such as a gyroscope or an acceleration sensor, isprovided inside the multifunction terminal 3500, display on the screenof the display portion 3504 can be automatically switched by determiningthe orientation of the multifunction terminal 3500 (whether themultifunction terminal is placed horizontally or vertically for alandscape mode or a portrait mode).

The display portion 3504 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken when thedisplay portion 3504 is touched with the palm or the finger, wherebypersonal authentication can be performed. Furthermore, by providing abacklight or a sensing light source which emits near-infrared light inthe display portion 3504, an image of a finger vein, a palm vein, or thelike can be taken. Note that the light-emitting device of one embodimentof the present invention may be used for the display portion 3504.

FIG. 34C is a perspective view of a security light 3600. The securitylight 3600 includes lighting 3608 on the outside of the housing 3602,and a speaker 3610 and the like are incorporated in the housing 3602.The light-emitting device of one embodiment of the present invention canbe used for the lighting 3608.

The security light 3600 emits light when the lighting 3608 is gripped orheld, for example. An electronic circuit that can control the manner oflight emission from the security light 3600 may be provided in thehousing 3602. The electronic circuit may be a circuit that enables lightemission once or intermittently plural times or may be a circuit thatcan adjust the amount of emitted light by controlling the current valuefor light emission. A circuit with which a loud audible alarm is outputfrom the speaker 3610 at the same time as light emission from thelighting 3608 may be incorporated.

The security light 3600 can emit light in various directions; therefore,it is possible to intimidate a thug or the like with light, or light andsound. Moreover, the security light 3600 may include a camera such as adigital still camera to have a photography function.

FIG. 35 illustrates an example in which the light-emitting element isused for an indoor lighting device 8501. Since the light-emittingelement can have a larger area, a lighting device having a large areacan also be formed. In addition, a lighting device 8502 in which alight-emitting region has a curved surface can also be formed with theuse of a housing with a curved surface. A light-emitting elementdescribed in this embodiment is in the form of a thin film, which allowsthe housing to be designed more freely. Therefore, the lighting devicecan be elaborately designed in a variety of ways. Furthermore, a wall ofthe room may be provided with a large-sized lighting device 8503. Touchsensors may be provided in the lighting devices 8501, 8502, and 8503 tocontrol the power on/off of the lighting devices.

Moreover, when the light-emitting element is used on the surface side ofa table, a lighting device 8504 which has a function as a table can beobtained. When the light-emitting element is used as part of otherfurniture, a lighting device which has a function as the furniture canbe obtained.

As described above, lighting devices and electronic devices can beobtained by application of the light-emitting device of one embodimentof the present invention. Note that the light-emitting device can beused for electronic devices in a variety of fields without being limitedto the lighting devices and the electronic devices described in thisembodiment.

Note that the structures described in this embodiment can be used inappropriate combination with any of the structures described in theother embodiments.

EXPLANATION OF REFERENCE

100: EL layer, 101: electrode, 101 a: conductive layer, 101 b:conductive layer, 101 c: conductive layer, 102: electrode, 103:electrode, 103 a: conductive layer, 103 b: conductive layer, 104:electrode, 104 a: conductive layer, 104 b: conductive layer, 111:hole-injection layer, 112: hole-transport layer, 113: electron-transportlayer, 114: electron-injection layer, 123B: light-emitting layer, 123G:light-emitting layer, 123R: light-emitting layer, 130: light-emittinglayer, 131: high molecular material, 131_1: skeleton, 131_2: skeleton,131_3: skeleton, 131_4: skeleton, 132: guest material, 140:light-emitting layer, 141: high molecular material, 141_1: skeleton,141_2: skeleton, 141_3: skeleton, 141_4: skeleton, 142: guest material,145: partition wall, 150: light-emitting element, 152: light-emittingelement, 170: light-emitting layer, 200: substrate, 220: substrate,221B: region, 221G: region, 221R: region, 222B: region, 222G: region,222R: region, 223: light-blocking layer, 224B: optical element, 224G:optical element, 224R: optical element, 260 a: light-emitting element,260 b: light-emitting element, 262 a: light-emitting element, 262 b:light-emitting element, 301_1: wiring, 301_5: wiring, 301_6: wiring,301_7: wiring, 302_1: wiring, 3022: wiring, 303_1: transistor, 303_6:transistor, 303_7: transistor, 304: capacitor, 304_1: capacitor, 304_2:capacitor, 305: light-emitting element, 306_1: wiring, 306_3: wiring,307_1: wiring, 307_3: wiring, 308_1: transistor, 308_6: transistor,309_1: transistor, 309_2: transistor, 311_1: wiring, 311_3: wiring,312_1: wiring, 312_2: wiring, 600: display device, 601: signal linedriver circuit portion, 602: pixel portion, 603: scan line drivercircuit portion, 604: sealing substrate, 605: sealant, 607: region, 607a: sealing layer, 607 b: sealing layer, 607 c: sealing layer, 608:wiring, 609: FPC, 610: element substrate, 611: transistor, 612:transistor, 613: lower electrode, 614: partition wall, 616: EL layer,617: upper electrode, 618: light-emitting element, 621: optical element,622: light-blocking layer, 623: transistor, 624: transistor, 683:droplet discharge apparatus, 684: droplet, 685: layer containingcomposition, 801: pixel circuit, 802: pixel portion, 804: driver circuitportion, 804 a: scan line driver circuit, 804 b: signal line drivercircuit, 806: protection circuit, 807: terminal portion, 852:transistor, 854: transistor, 862: capacitor, 872: light-emittingelement, 1001: substrate, 1002: base insulating film, 1003: gateinsulating film, 1006: gate electrode, 1007: gate electrode, 1008: gateelectrode, 1020: interlayer insulating film, 1021: interlayer insulatingfilm, 1022: electrode, 1024B: lower electrode, 1024G: lower electrode,1024R: lower electrode, 1024Y: lower electrode, 1025: partition wall,1026: upper electrode, 1028: EL layer, 1028B: light-emitting layer,1028G: light-emitting layer, 1028R: light-emitting layer, 1028Y:light-emitting layer, 1029: sealing layer, 1031: sealing substrate,1032: sealant, 1033: base material, 1034B: coloring layer, 1034G:coloring layer, 1034R: coloring layer, 1034Y: coloring layer, 1035:light-blocking layer, 1036: overcoat layer, 1037: interlayer insulatingfilm, 1040: pixel portion, 1041: driver circuit portion, 1042:peripheral portion, 1400: droplet discharge apparatus, 1402: substrate,1403: droplet discharge means, 1404: imaging means, 1405: head, 1407:control means, 1406: space, 1408: storage medium, 1409: image processingmeans, 1410: computer, 1411: marker, 1412: head, 1413: material source,1414: material source, 2000: touch panel, 2001: touch panel, 2501:display device, 2502R: pixel, 2502 t: transistor, 2503 c: capacitor,2503 g: scan line driver circuit, 2503 s: signal line driver circuit,2503 t: transistor, 2509: FPC, 2510: substrate, 2510 a: insulatinglayer, 2510 b: flexible substrate, 2510 c: adhesive layer, 2511: wiring,2519: terminal, 2521: insulating layer, 2528: partition wall, 2550R:light-emitting element, 2560: sealing layer, 2567BM: light-blockinglayer, 2567 p: anti-reflective layer, 2567R: coloring layer, 2570:substrate, 2570 a: insulating layer, 2570 b: flexible substrate, 2570 c:adhesive layer, 2580R: light-emitting module, 2590: substrate, 2591:electrode, 2592: electrode, 2593: insulating layer, 2594: wiring, 2595:touch sensor, 2597: adhesive layer, 2598: wiring, 2599: connectionlayer, 2601: pulse voltage output circuit, 2602: current sensingcircuit, 2603: capacitor, 2611: transistor, 2612: transistor, 2613:transistor, 2621: electrode, 2622: electrode, 3000: light-emittingdevice, 3001: substrate, 3003: substrate, 3005: light-emitting element,3007: sealing region, 3009: sealing region, 3011: region, 3013: region,3014: region, 3015: substrate, 3016: substrate, 3018: desiccant, 3500:multifunction terminal, 3502: housing, 3504: display portion, 3506:camera, 3508: lighting, 3600: light, 3602: housing, 3608: lighting,3610: speaker, 8000: display module, 8001: upper cover, 8002: lowercover, 8003: FPC, 8004: touch sensor, 8005: FPC, 8006: display device,8009: frame, 8010: printed board, 8011: battery, 8501: lighting device,8502: lighting device, 8503: lighting device, 8504: lighting device,9000: housing, 9001: display portion, 9003: speaker, 9005: operationkey, 9006: connection terminal, 9007: sensor, 9008: microphone, 9050:operation button, 9051: information, 9052: information, 9053:information, 9054: information, 9055: hinge, 9100: portable informationterminal, 9101: portable information terminal, 9102: portableinformation terminal, 9200: portable information terminal, 9201:portable information terminal, 9300: television set, 9301: stand, 9311:remote controller, 9500: display device, 9501: display panel, 9502:display region, 9503: region, 9511: hinge, 9512: bearing, 9700:automobile, 9701: car body, 9702: wheel, 9703: dashboard, 9704: light,9710: display portion, 9711: display portion, 9712: display portion,9713: display portion, 9714: display portion, 9715: display portion,9721: display portion, 9722: display portion, 9723: display portion.

This application is based on Japanese Patent Application serial no.2015-103759 filed with Japan Patent Office on May 21, 2015, the entirecontents of which are hereby incorporated by reference.

The invention claimed is:
 1. A compound comprising: a first highmolecular chain and a second high molecular chain each comprising: afirst skeleton comprising at least one of a π-electron richheteroaromatic skeleton and an aromatic amine skeleton; a secondskeleton comprising a π-electron deficient heteroaromatic skeleton; athird skeleton where the first skeleton and the second skeleton arebonded to each other through the third skeleton; and a fourth skeletonconfigured to emit light, wherein the first high molecular chain and thesecond high molecular chain are configured to form an excited complex.2. The compound according to claim 1, wherein the π-electron richheteroaromatic skeleton comprises at least one of a thiophene skeleton,a furan skeleton, and a pyrrole skeleton.
 3. The compound according toclaim 1, wherein the π-electron deficient heteroaromatic skeletoncomprises at least one of a pyridine skeleton, a diazine skeleton, and atriazine skeleton.
 4. The compound according to claim 1, wherein thefourth skeleton is configured to exhibit fluorescence.
 5. The compoundaccording to claim 1, wherein the fourth skeleton is configured toconvert triplet excitation energy into light emission.
 6. The compoundaccording to claim 1, wherein the fourth skeleton is configured toexhibit phosphorescence.
 7. The compound according to claim 1, whereinthe fourth skeleton is configured to emit light with a wavelengthgreater than or equal to 400 nm and 680 nm.
 8. The compound according toclaim 1, wherein the third skeleton comprises at least one of a biphenylskeleton and a fluorene skeleton.
 9. The compound according to claim 1,wherein the first skeleton in the first high molecular chain and thesecond skeleton in the second high molecular chain are configured toform an excited complex.
 10. The compound according to claim 1, whereinthe excited complex is configured to exhibit thermally activated delayedfluorescence at room temperature.
 11. A lighting device comprising thecompound according to claim
 1. 12. A light-emitting device comprisingthe compound according to claim
 1. 13. The light-emitting deviceaccording to claim 12, wherein the light-emitting device comprises alight-emitting layer, and wherein the light-emitting layer comprises thecompound.
 14. An electronic device comprising the light-emitting deviceaccording to claim 12.